M1919  History
Barrels and Jackets
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In this segment  we are going to discuss the M1919 family's assembly that houses the internal parts of the caliber .30 Browning machine gun.

The bottom plate, top plate and trunnion block assembly have been covered in detail in previous articles in this series. 

This offering will consist of the right and left side plate assemblies, breech cam lock and cam lock screw. 

We will also address the development of the at least three short round stops their function, belt holding pawl, bracket and pin, feed extractor and extractor cams and front and rear cartridge stops.

Most U.S. Army Ordnance publications refer to the portion of the weapon that houses the  internal working parts as the "receiver".  

It is most often a single piece that connects the barrel and various other parts of the weapon allowing them to function as a firearm.

Some weapons, like the M16 rifle, consist of a two part receiver the upper, which is attached to the barrel and houses the bolt and bolt carrier groups and the lower which houses the fire control and buffer groups and is attached to the butt stock.
Most times though, when we say "receiver" we picture something along the lines of the M1903 Springfield, M1 rifle or M1 carbine receiver. 

In our mind's eye we see a chunk of steel that has been forged and machined to connect the various parts of the weapon.

In most cases Ordnance saw things the same way.

Somewhere in Ordnance archives there is a "style book" or some publication that describes, likely in great detail, how to name things the Army way.

In other words a naming convention that applies the same word or words to all things Ordnance.

It is not presently known exactly why Ordnance decided to call the "receiver" of the M1917, the parent of the subject of these articles a "casing".

The term "casing" may have been chosen because the "receiver", in this instance, is fabricated from multiple parts, and Ordnance was seeing the forged chunk of steel and decided that the image didn't fit the subject at hand and this steel box did encase the working parts.

In any event, the combination of parts that make up the "receiver" of the M1919's is officially referred to as "CASING, assembly, followed by the model number of the particular weapon i.e.  CASING, assembly, M1919A4

Ordnance sometimes used the term "assembly" to indicate a series of parts attached to each other either by necessity or functionality.

The right and left side plates and the trunnion are assemblies.

The M1917 and its M1919 derivative's casing assemblies are an assembly of assemblies.

This is C64222 Revision 9 (12-10-45) the left side plate assembly drawing originally adopted on March 10, 1939.

This assembly was used on M1919A4, M1919A5 and M1919A6 weapons.

The M1919A2 used a virtually identical left side plate C64005.

Side plates were not required to be piece marked, however you may encounter some plates with "L" imprinted inside the left side plate.

These "L" imprinted side plates were produced during WWI by the New England Westinghouse Company.

The right side plates were marked with "R", however since the right side plate is the controlled part, and is removed during the de-militarizing process we seldom encounter them.

At various times during WWII and shortly thereafter some of the side plate assembly components were available as replacement parts but many weren't.

The box on the lower left of the drawings indicated which parts were not available for field maintenance by marking them with an asterisk.

You could get either of the extractor cams along with their attaching rivets, the two short mount adaptor rivets, but not the long rivet that passed through the trunnion or the mount adaptor itself.

You could not order the entire side plate assembly or the side plate either.

This seemingly bizarre position on which parts could be replaced and which parts couldn't  had a reason.

That reason was that the field forces were not equipped to replace the entire side plate assembly and by association the side plate, belt holding pawl bracket and even the mount adaptor because it was riveted through the trunnion.

Many of the rivet holes were reamed at assembly to fit the particular set of parts at hand.

This was done in an assembly jig to hold the parts in the proper alignment.

Ordnance field forces were not equipped with these tools.

However field depot personnel could replace the two mount adaptor rivets and the rivets that held on the belt holding pawl bracket and the cams and their attaching rivets if the occasion arose because they were equipped with various rivet sets and anvils.

After WWII, starting in about 1947, the Ordnance Department took a different view of things and further restricted the issue of some parts for field repair because we were not at war and centralizing ordnance repair into depots was deemed more efficient.

Some assemblies like the extractor assembly for the Browning's were user replaceable  units of issue.

If you had an M1919A4 extractor with a broken ejector you replaced the entire extractor assembly.

While ejectors were listed as replaceable parts,  users of the weapon didn't have the ability to change them.

One of the things that complicates any dialogue dealing with M1919's is that many early M1919A4's were rebuilt from other weapons such as the 1300 or so 18 inch barreled M1919 Tank Machine Guns, various models of caliber .30 aircraft guns, M1919A2's and a good percentage of the almost 70,000 M1917 water cooled weapons left over from WWI.

Even at this late date nearly 80 years after the fact some of these converted weapons are still surfacing as "parts kits" which are the basis for most all of the semi-auto replica firearms being produced today.

While the right side plate, the part that the ATFE considers the receiver and is the controlled part that is destroyed, the left side plates of many of these converted weapons live on to ever bedevil their owners.

Extra holes, slots and special bottom plates used in the conversion process for both the M1919's and the M1917A1's still exist in sufficient number to raise all kinds of questions.

The two photos above, courtesy of Amish-bob/Ordnance Research Inc., show the inside and outside of a refinished left side plate that originally belonged to a M1917 water cooled machine gun equipped with a panoramic sight base.  This weapon underwent the stirrup reinforcement modification and conversion to a M1919A4 probably serving in WWII maybe Korea and who knows where else along  with a stint with the Israeli Defense Forces.

The faint 7.62 and upside down "square U", an IDF property mark that appears at the top of the plate in the lower picture show IDF conversion to 7.62X51 NATO caliber.

Talk about your world traveler!

The second and fourth holes from the right (front of the weapon) in the top picture or from the left in the bottom picture  were for the reinforcing  stirrup retrofitted to  almost 26,000 M1917 Brownings post WWI to correct design deficiencies that appeared during WWI combat use.

These problems are discussed in the Bottom Plates tab in this set of articles along with the development of the D35392 flanged bottom plate that uses the other 8 holes on the bottom of the plate, shown in the above pictures, for attachment rivets.

The slot near the bottom of the plate accommodated the "dovetail" slip in bottom plate a  feature of the original M1917 carried over into the tank guns and subsequent derivative designs of the M1919A2 and early prototype A4's, finally being replaced by the flanged bottom plate mentioned in the paragraph above.

This particular sample has the C45965 rear sight base that dates from March 10, 1939, a feature of production M1919A4's

Normally the rear sight base has the three holes for mounting optical sight base drilled and tapped in the base before mounting to the left side plate.

In the top picture it appears that the optical sight mount bolt holes were drilled after the rear sight base was riveted to the left side plate resulting in the bolt holes going completely through the side plate.

None of these "extra" holes or slots were present in left side plates for purpose built production weapons shown in the first drawing in this article which only has the rivet holes to mount the rear sight base.

This 1936 photo courtesy of the RIA Museum, Jodie Creen Wesemann, shows a very early pre-production M1919A4 with a reinforcing stirrup and rear sight base mounted on the top cover latch along with the 24 inch slotted barrel jacket.

While we are on the subject of "extra" holes in side plates, here's an Israeli Defense Force modified left side plate.  Most of the parts kits available today are former IDF weapons that the U.S. supplied to Israel as military assistance items.

This is a Saginaw Steering Gear produced WWII vintage weapon probably late 1943 to mid 1944. 

Note the number of cast parts and the different color of the Parkerizing at the rear of the side plate caused by heat treatment of the rear most inch.

The IDF converted these weapons to 7.62X51 NATO caliber and during the process made a few modifications to the weapon to improve function with ammunition that it  was not originally designed to use.

The extra hole in the left side plate has caused much speculation in the M1919 community.

Most believe, as I do, that the hole, because it is almost directly opposite from the bolt latch rivet, was there to allow the bolt latch rivet on the right side plate to be tightened.

The main difficulty with the rivet tightening theory is that the U.S. Ordnance Department designed a tool for that very purpose that did not require the drilling of holes in the left side plate.

The tool for tightening the bolt latch rivet on already assembled weapons can be seen at the Bolt Latch tab in this series of articles.

On new built weapons the bolt latch was likely fastened to the right side plate before it was assembled to the rest of the casing parts.

While the bolt latch and the attaching rivet was eliminated from production requirements in late May of 1943, by this date about 65%, depending on whose figures you use, of total M1919A4 production had been achieved.

This means that more M1919A4's had the latch than didn't.

M1919A4's rebuilt under Ordnance supervision after August,1949 should have had the  bolt latches removed.

Most of the parts kits advertised include a bolt latch, which some think is a "safety" which it most definitely is not.

One of several things could explain this situation.

Most of the weapons the IDF received had bolt latches, which would mean that none of these weapons went through an Ordnance supervised rebuild which smells a little fishy, or that the IDF liked the idea of the bolt latch and added them to weapons where they had been removed or never installed requiring the hole in the left side plate to peen the rivet.

Since bolt latches were never required to be, and are seldom marked with, piece marks or manufacturers identification codes it is difficult to know who made the latches or installed them. 

Another theory is that the IDF drilled out the bolt latch rivet, removed the latch and using the right side plate rivet hole as a pilot drilled through the left side plate as part of a fixture to hold the casing while cutting the belt holding pawl slot to the new dimension for the 7.62 pawl.

They then replaced the bolt latch and used the left side plate hole to peen a new rivet. 

Further muddying the waters is the fact that some IDF marked parts kits don't have the extra hole and some have an additional hole above and to the rear of the left mount adaptor.

The contrarian school of thought believes that the hole has something to do with setting head space because the Israeli 7.62 barrel had a different design barrel locking notches and a different barrel locking spring that makes setting head space by the USGI method somewhat difficult unless you have three hands.


The 7.65X51 NATO cartridge (front) is about 1/2 inch shorter than the U.S. Caliber .30 cartridge (rear) which required feed way spacers to properly position the cartridge for extraction from the feed belt.


To prevent feeding problems the IDF designed a slightly wider belt holding pawl which required that the belt holding pawl bracket, left side plate and trunnion cuts to be made wider to accommodate the 7.62 pawl.

This photo shows the tool marks from the cut, made with the casing assembled, that altered the pawl opening. 

The weapon shown has a USGI Caliber .30  front and rear cartridge stops and a IDF modified bolt, top cover and belt feed slide and pawl.

This photo, courtesy of Rollin Lofdahl, shows a comparison of the IDF modified pawl bracket  in the upper half of the photo and the USGI unmodified bracket in the lower along with their matching pawls, springs and pawl pins. 

The IDF appears to have used a slightly different pawl spring which applied more upward pressure to the pawl. 

This heavier IDF spring sometimes causes feeding issues in semi-auto M1919 semi-auto conversions requiring either a different spring or removing one or two coils from the IDF spring.

It is not known why the IDF opted for the heavier spring.

Most IDF pawls can be identified by the marking on the outside edge which is two Hebrew characters in an oval followed by "7.62".

The IDF modified pawls and other feed system parts, other than the feedway spacers work equally well with U.S. caliber .30 ammunition.

The split pin that holds the belt holding pawl in place, used on all of the air cooled ground Caliber .30 Brownings and the M18A1 and M19 aircraft guns, remained virtually the same from the 51-10-29 drawing for the M1917 water cooled originally dated June 13, 1917 and then became A20566 in 1931 and finally B147217 on to the end of its service life. 

The only real change was the material from which the pin was made, originally drill rod which didn't require heat treatment and later W.D. 1095 steel using various hear treatments and protective finishes.

Odd bits of information always seem to surface when examining these old drawings.

The original drawing of the pawl pin, 51-10-29, was submitted to the Ordnance Department by the Link-Belt Co. of Philadelphia, PA

It is not presently known what the relationship of Link-Belt, who in the WWI era was a manufacturer of conveyors and agricultural machinery and in later years as a subsidiary of FMC Corporation manufactured construction cranes and excavation equipment, was to U.S. Army Ordnance.  

In addition to the modifications made by the IDF, there are differences in the appearances of the belt holding pawl brackets manufactured by US makers.

The following three photos, courtesy of Rollin Lofdahl illustrate some observed differences between manufacturers.

   This Remington manufactured bracket was likely from a M1917 water cooled Browning.

Another WWI Vet.

This bracket is from a WWII vintage Saginaw M1919.

Despite the differences in appearances of brackets from various manufacturers, other than the second and third  IDF modified brackets, they are functionally the same.

The brackets also have rectangular cuts forward and aft of the belt holding pawl cut.

The front cut, along with the pawl pin is used to fasten on the "live round stop".

Ordnance developed a blank firing adaptor that replaced the muzzle plug/front barrel bearing that allowed the weapon to function using blank ammunition. 

Since blanks provide very little recoil energy this system relied on increased gas pressure against the front of the barrel, rather than the usual recoil operated/gas assist operation with service ammunition.

The adaptor had a very small muzzle opening to create sufficient back pressure to cycle the weapon. 

The muzzle opening was so small that it would not allow a projectile to pass through, and to prevent anything other than a blank from entering the feed way and creating a potentially lethal situation, the live round stop was installed first and removed last when converting the weapon to blank firing operation.

Often the blank firing device on the muzzle, and the outer end of the live round stop were marked with a brightly colored paint as a method of visually confirming that these devices were correctly installed.

In the late 1930's the Army, who at that time was operating the air force which they  called the Army Air Corps, decided that .30 caliber machine guns lacked the necessary power and range for either offensive or defensive armament on aircraft  and settled on the Browning .50 caliber as the weapon of choice for  Army aircraft.

This meant that a sizable number of .30 caliber aircraft type machine guns became surplus and were thrown into the pool of weapons to be rebuilt. 

A number of these aircraft models were converted into M1919A4, A5 and possibly A6 weapons.

The obsolescence of the Caliber .30 aircraft weapons increased the number of possible permutations of casing assemblies available for rebuilding into more desirable weapons.

This photo courtesy of "gearlogo", m1919a4.com forum, shows a left side plate from a M1918 (Model of 1918) Browning Aircraft Machine Gun that had the two synchronizer cuts filled with steel plate and the two extra rivet holes for the reinforcing stirrup, and the "dovetail" bottom plate slot. 

The outside of this plate has IDF property marks and was imported into the U.S. as a "parts kit".

This weapon has had more lives than the proverbial cat.

Early in WWI when single seat aircraft first appeared, pilots shot at each other with revolvers, shotguns, and most anything else that would go bang.

Later, they were armed with machine guns installed in a fixed forward firing position on the top of the upper wing so that the line of fire did not strike the propeller.

This type of mounting made it difficult for the pilot to aim, fire and clear jams or even reload the weapon.
The answer was machine guns mounted on the cowl of the aircraft directly in front of the pilot.

The drawback to this mounting location was the considerable problem of shooting off your own propeller.

The French solution to this problem, and I'm not making this up, was to install metal deflector shields on the propeller blades. 

In 1914, Anthony Fokker, a Dutch designer of German aircraft, devised a better system of preventing you from shooting yourself down. 

He developed a method of interrupting the fire of a machine gun while the propeller blades were obstructing the line of fire.

These devices were called, not surprisingly, interrupters or "synchronizers".

They worked on a mechanical linkage between the engine crankshaft and the firing mechanism of the weapon and prevented the weapon from firing when the propeller blades were in the line of fire.

This cut from drawing 51-16-5 dated November 1, 1918, 10 days before the Armistice ending combat in WWI, shows the M1918 aircraft left side plate with openings for the synchronizer.

This cut from a RIA Museum, Jodie Creen Wesemann, provided photo, dated February 9, 1942, shows an obsolete Caliber .30 Aircraft gun, probably a M1918, converted into something more useful first a M1919A4 then a M1919A5.

Unfortunately, the armorers at RIA did a very good job of obliterating the model number on this New England Westinghouse built aircraft gun.
The belt holding pawl underwent very few changes in its service life.

Drawing B147216 Revision 10, 7-31-44, the belt holding pawl.

Note the "Alternative" method of manufacture on the left.  Apparently, the recess for the pawl spring originally was cut with some sort of special tool that left a flat bottomed hole.

On December 2, 1942 Saginaw Steering Gear suggested that using a standard 3/32 drill bit would accomplish the same thing without making some special tool.  Revision 7, 1-6-43 to the this part drawing adopted that suggestion as the alternative.

Saginaw was forever suggesting ways to decrease cost/increase production like the simple expedient of using a commonly available drill bit in place of a special made tool.

This is Saginaw's drawing suggesting the use of the drill bit dated 12-2-42 ordnance adopted this suggestion as an alternative method of manufacture 5 weeks later.

Note the conical area at the top of the spring recess cut caused by the use of the drill bit.

Some times while looking for something, you find a nugget of information.

Here's one of those nuggets found by Jodie Wesemann while copying drawings that I had requested.

Apparently Chrysler's Amplex Division, formed in 1927 to produce "Oilite" sintered copper/tin/graphite bearings requiring no external lubrication, produced some M1919 parts, or at least belt holding pawls.

This drawing suggests that some of the pawls produced by Amplex  did not meet Ordnance Department requirements and the drawing was produced to show the variance from specification.

Someone at RIA hand wrote B147216 and filed this drawing with the other "Backfile" drawings of this part.

The final left side plate components are the extractor feed cam and the extractor cam.

Rollin Lofdahl photo

On the left is the extractor feed cam B17469 and on the right is the extractor cam C8452.

The parts are shown in their correct relationship when installed on the inside of the left side plate.

The purpose of these parts is to guide the extractor assembly, by means of the spring loaded extractor cam plunger in the extraction/feeding cycles of the weapon.

The extractor feed cam is another of those parts that underwent virtually no change in appearance.

However there were changes to material which caused changes to heat treatments.

The original part was forged from "C" steel, when this part was converted to letter prefix drawing in 1931 the material was changed to W.D. 1035 steel with no required heat treatment.

This cut from drawing 51-10-11 was another drawing submitted by our friends at Link-Belt.

It is likely that Link-Belt provided drafting room support to the Ordnance Department during WWI, but is not known with any certainty.

Revision 3 to B17469 (2-1-38) changed the material to W.D. 1050 and required heat treatment of the entire part. This revision also changed the piece mark of the part to B17469-3.

Revision 7 (6-18-42) changed the material yet again and removed the requirement for heat treating the entire part in favor of case hardening and annealing the  front (right) half inch.

This revision did not result in changing the piece mark suffix.

Why this is so in Revision 3 and not Revision 7 is not clear.

This business of changing materials and heat treatments likely were an attempt to ease manufacturing and increase production while conserving critical materials, labor and            shop/ machine time.

You will note at the upper rear (left in the drawing) a small semi-circular cut.

The purpose for this cut is believed to provide a "parking notch" for the extractor cam plunger on the left side of the extractor assembly.

Pulling the bolt to the rear and manually aligning the plunger in this cut would catch the bolt and prevent the it from closing until the bolt handle was pulled slightly to the rear and released.

I do not believe this to be a particularly good method of bolt hold back as the slightest bump can dislodge the bolt usually resulting in some smashed fingers if they happen to be in the wrong place.

Rollin Lofdahl photo
This illustration shows the two styles of extractor cam commonly seen

Drawing 51-10-23 at the changeover to letter prefix drawing C8452 June 1, 1931.

The lower style pictured in the photo is the original design shown in drawing 51-10-23.


The upper extractor in the extractor cam photo dates from Revision 14 to drawing C8452  (December 18, 1943).  This change which altered the appearance but not the functionality of the part did not change the suffix number of the piece mark which remained C8452-12. 

This change in design was considered "optional" at the discretion of the manufacturer and the Ordnance District supervising the production.  Since the basic drawing number C8452 never changed, all of the parts regardless of appearance or piece mark suffix were considered useable. 

It is entirely possible that the early style extractor cam remained in production long after the December 18, 1943 date shown on Revision 14.

The extractor cam also underwent the usual heat treatment and steel type changes in the place of forging as shown for the original design part in a continuing effort to speed up production and simplify manufacture.  Apparently the removal of the small lip that was intended to help guide the extractor was considered unnecessary.

Original drawing C64222 (March 10, 1939).

The title block in the upper right corner is a little hard to read, but the 'Drg Pertains To" block lists the M1919A4 Fixed and Flexible and the casing assembly which was common to both models.

Drawing D35411 Revision 14 (5-31-43).

Revision 14 removed the hole for the bolt latch rivet and changed the piece mark suffix to -14.

This drawing is a little dark, however you can make out the Revision 4 and Revision 10 notations in the upper left hand corner.

Revision 3 (9-3-40) added the heat treating requirement for the rearmost 1 inch of the right side plate and Revision 10 (6-18-42) dropped the early description for the method of heat treating and just substituted the phrase "heat treat" added the requirement to "anneal around two holes" which are the two rearmost rivet holes one for the rear top plate rivet and one for the rear bottom plate rivet.


Drawing C90722 Revision 2 (1-27-43).

The M1919A5 had its own drawings for the right side plate side, right side plate assembly and the casing assembly.

The only difference in the assemblies are the side plates the M1919A5 had four extra holes for the retracting handle guides no bolt latch rivet hole and was marked M1919A5.

This only holds true for purpose built A5's. Many obsolete aircraft and some rebuilt and new made M1919A4's were converted to 1919A5's and their side plates were hand stamped with the new designation. 

The M1919A5 was a special purpose weapon that went out of production in mid 1943 because the its primary use was on the M3A1 Stewart light tank that was already obsolete when it entered combat in North Africa in 1943. 

There are very few if any unaltered purpose built A5's in existence most were converted into something more useful. 

Conversion to other uses did not require the filling of the four holes required for mounting the retracting handle guides so their original configuration sticks out like a sore thumb.


Drawing C94516 Revision 1 (3-11-44) the right side plate assembly for the M1919A6.

The only observable difference between this right side plate and the D35411-14 M1919A4 right side plate is the markings.

All of the M1919 right side plate assemblies, along with the M1917 and M1917A1 used the same front and rear cartridge stops, mount adaptors (sometimes referred to as "pintle pads") and attaching rivets.

Design of the cartridge stops attached to the right side plate remained pretty much constant except for changes in steel types.

Drawing A24603 Revision 11 (7-22-43).  Revision 1 to this drawing changed the steel type from WD 1095 to WD X1335 other than that the actual appearance of the stop never changed.

This design provided a self rivet feature. 

The front cartridge stop hole in the right side plate was chamfered at 60 degrees on the exterior side and the shank of the stop was inserted from the inside and peened into the plate and finished flush.



Drawing B131258 Revision 9 (7-31-44).

Revision 9 was an administrative action which merely cleaned up the previous revisions likely to make the drawing more legible. 

The original drawing dated June 1, 1931 was the conversion drawing from the old Class and Division system to the "new" letter prefix style and showed the part being made from WD 1325 steel with no heat treatment.  Revision 3  (2-1-38) changed the steel type to WD 3115 and added the heat treatment requirement. 

Revision 6 (6-18-42) replaced the specific heat treating instructions with the generic "Heat Treat" and the changed the Rockwell Hardness from 34-46 to 34-40.

Many Ordnance small arms drawings have this same 6-18-42 date that removed the specific heat treating instructions and changed the steel type likely because the method  shown on the drawings became part of the contract specifications for the part. 

Hardening the part could be done in many different ways and the manufacturers likely complained about being contractually obligated to one method.

The original drawing also did not require piece mark imprinting which occurred as the result of Drawing B169913, the list of parts and manufacturer codes required to be marked issued in April of 1940.  This drawing is reproduced in the Markings article on this site.

This cut from drawing 51-10-10 dated June 1, 1931 is the last Class and Division drawing before conversion to the letter prefix drawing B17462.

The mount adaptor, which remained constant in design, was attached to both sides of the casing assembly providing wearing surfaces.  Note that the hole in the center called out at a diameter of .5615 was reamed to 9/16 (.5625) after assembly to the trunnion.

After Revision 4  (11-8-40) to the side plate drawing D35410 all of the mount adaptor holes and the rivet holes for attaching the bottom plates were reamed to final diameter at assembly to the side plates, trunnion and bottom plate, this procedure eased assembly and ensured a better fit of the parts.

The USGI bolt that attached the pintle to the weapon was 9/16.

IDF modified weapons often have the pintle bolt hole in the casing reamed to 5/8 inch, probably to relieve worn holes and true the bore alignment with the pintle. 

The purists among us often sleeve the 5/8 hole back to original USGI diameter. 

One thing to keep in mind is when assembling a parts kit is to be aware that the mount adaptors furnished with the kit might not have the same size hole and most semi-auto right side plates have 9/16 pintle bolt hole.


D35410 Feb 1, 1938 this drawing cut shows the left side plate for a M1917 with the mount adaptor integral with the side plate. 

This method of fabrication would involve machining off the entire side plate exterior surface leaving just the small area of the mount adaptor.  Why this method of fabrication was actually considered is unknown.

 Revision 4 (11-8-40) reverted back to the separate mount adaptor riveted to the side plate.  There are not likely very many of this style of side plate/mount adaptor in existence.

This rather bad photo taken at the RIA Museum is the style of side plate mount adaptor shown in the drawing D35410 above.  Note the tapered surface of the adaptor. 

Drawing 51-10-18 the breech lock cam at conversion to letter prefix drawing June 1, 1931.

Originally this part was forged from "C" steel, the replacement drawing B17467 changed the steel type and on February 1, 1938 this drawing was replaced by C64133. 

The change in drawing numbers was likely driven by a need to show the part in a larger scale which required a larger medium on which to depict the part.

The rectangular boss on the bottom of the cam fits into a cut on the bottom plate to locate the cam.  This version has no staking slots for the lock screw.  Depot Maintenance Work Requirements published in 1970 requires all breech lock cams to have two staking notches.


C64133 also changed the steel type and added the elaborate description of heat treatment shown in the upper left.  This drawing and all subsequent drawings, requires piece marking on the bottom surface of the part.   



Drawing C64133 Revision 16 (8-7-45). 

Revision 15 made a couple of minor dimension/tolerance changes and Revision 16 added a 30 degree taper to the outside edges of the bottom surface of the part.

Many Ordnance drawings, like this example, eliminate heat treating different surfaces of the part in different ways as shown on the original C64133 drawing. 

This was often accomplished by changing the steel type and treating the entire part.

These changes likely saved a considerable amount of time and produced more uniform parts.

You will notice that Revision 15  drawing has two notches in the top surface of the cam at the screw hole.  These staking notches were added by Revision 7 (3-16-42).


This DWO added the staking slots and revised a few other dimensions on the drawing of  the breech cam lock.  Sometimes these documents have a reason for the change spelled out in the text, however, this one only has the O.O. letters of authorization.

The " O.O.TT" numbers are the Teletype message numbers followed by the message origination time ( EWT is Eastern War Time a sort of year around Daylight Savings Time used until September 30, 1945) and the initials of the person sending the message.

Teletype was the only apparent method of transmitting text messages in near real time and appears to have been used only in cases of critical changes.

Because of fear of  damage to the breech lock cam or the bottom plate, it was decided to back the screw off from hand tight 1/6 to 1/4 turn and staking the screw to the cam to prevent the screw from loosening to the point of falling out. 

TB ORD 366, the small arms rebuild manual (July, 1949), describes the results of this procedure as: "There will be perceptible float of the cam".  

This was a requirement on all M1919's produced by RIA and Buffalo Arms, however, it was optional on Saginaw Steering Gear produced weapons.

For reasons not clear at this time, the Saginaw produced weapons breech lock cam screws were allowed to be drawn up tight and staked. 


This cut from drawing 51-10-24 is the drawing superseded by the letter prefix replacement A20605.  The SNL's from 1940, 1943 and 1944 call this the "thin-hd" screw and it was classed as "useable" until the publishing of the April, 1947 SNL when it was no longer listed as an available part.

Note the concave area at the end of the screw to make the screw easier to stake to the cam.

Drawing A20527 (April 4 1927) the original drawing of the cam lock screw.  This part was intended for use on the M1919 Aircraft Machine Gun.

The SNL's from 1940, 1943 and 1944 refer to this part as the "thick-hd" screw and the "preferred" part for all of the M1919's.

All of the illustrations in the SNL's show the A20527 drawing/part number.

Goldsmith in Volume 1 of The Browning Machine Gun presents some interesting pictures of experimental cast casings for the M1919's.  The cast casing (Figure 429, 430 and 431 pp 398, 399 and 400) was tested in late 1942 along with a few other cast parts developed by Saginaw. 

The cast parts were adopted, however the casing design, while apparently successful, was not.

Dolf also had a picture of the "RIA Idealized M1919A4" that he obtained from the Springfield Historical Site dated 1951 that appears as Figure 516 pp 477.

The SHS photo appears to be a version of the 7 digit conversion drawing 7144037 Sheet 2 Alternate Construction "A".

Drawing 7145465 Sept 7, 1951 the original 7 digit drawing of the cast casing now called "Body, Casing".

This drawing was changed by revision "C" (10-28-53) which added two 10-32 holes and altered the profile of the right side in the area of the feed way to allow the attachment of a Stop assembly that held the front cartridge stop on a steel plate rather than rivet the front cartridge stop directly to the casing body.

You will note that this is an "F" size drawing.

Just to keep things interesting, or for a lack of something better to do, Ordnance changed the size of drawing mediums again in about 1952 and the new "F" size 28X40 replaced the old "D" size 24X40  The old "D" size became 22X34 and the rest of the letter sizes also changed.

Apparently, the cast casing never really went away, even after it wasn't adopted in 1942, and later resurfaced as part of a modernization program for the M1919's.

This is a cut of the upper left corner of drawing 7145465 showing the proposed markings .

Note that the final model number designation is blank allowing the use of this part as either a A4 or A6 as the A5 had been out of production since about April 1943.

This cast body had the trunnion, mount adaptors, bottom plate and T&E attaching points integral with the casting but used the original rear cartridge stop and rivet, extractor cams, top plate, rear sight base, breech cam lock, and screw.

The cast body also provided for a reinforced area at the rear, formerly heat treated on the right and left side plates, where the back plate slipped into the mounting grooves.


Drawing 7114037 Sheet 2 showing the "Alternate Construction "A" the cast body. This drawing is also dated September 7, 1951.

Note the instruction to stamp a "6" in the marking area to designate the model number.

This version of the cast body or casing required the use of a Stop assembly A8408715 consisting of a steel plate with the A24603 front cartridge stop attached and two 10-32 mounting screws (BCLX1.9) which were required to be staked to the plate.

This change in design likely was required because of the rather thin area of the casting where the front cartridge stop attaches and the fact that the front cartridge stop could be replaced by field forces replacing the plate assembly, which had the stop already attached without riveting a replacement stop to the cast casing itself and possibly breaking the casting.

Sheet 1 of 7114037 is a conventional casing assembly for the M1919A6.

There is an identical set of these drawings, which in early 1951, replaced the old Class and Division drawings used as finding diagrams for the M1917A1, M1919A4 and the M1919A4E1.

Engineering Change Order 36451, apparently used as a transmittal letter, to accompany the drawings of the new cast casing assembly dated 28 September 1951 which provided for the  alternate method of manufacture.

The authorizing authority was a  serialized letter from the Office of the Chief of Ordnance (O.O.472.5/162)  dated 5 March1951 ordering the change (Revision 7) to be effective 9-7-51.

Ordnance maintained the drawings of the cast body until at least mid 1954, by this time the M1919's end of service life was on the horizon.

Since Ordnance had thousands of conventional M1919 casings it is not likely that other than a few tool room samples of the cast body were ever produced.

The Army including the Ordnance Department struggled mightily with the problem of date notation.

In the U.S. we usually use a notation system of month-day-year i.e. November 2, 2010 or       11-2-10.

However, most European nations including Britain used a system of day-month-year i.e.         2 November 2010  or 2-11-10. 

It is easy to see the potential to misinterpret the notation of  2-11-10 or 11-2-10 is it February 11th or November 2nd ?

During WWII the U.S. Armed Forces adopted the method of using day-month-year that everyone else was using except they always used alpha characters for the month.

It would be difficult to confuse the date written 11 February 2010 with 2 November 2010.

Drawings seemed to have always maintained the month-day-year method of notation whether or not the month was denoted in alpha characters or digits.

The ECO presented above shows Ordnance having it both ways.

Another casing part that became a post WWII requirement was the short round stop.

Drawing B7162248 (March 6, 1946) the original design short round stop. 

The exact reason for the development of this part remains something of a mystery.  

Where the "short rounds" were coming from? 

The Ordnance department never changed the physical dimensions for the M2 Ball projectile or cartridge or as far as we can tell any of the other Caliber .30 ammunition used in this weapon.

However the short round stop performs as advertised when attempting to use commercial .30'06 ammunition which tends to be some what shorter than military ammo.

One reason for this development could have been the increased use of metallic links by ground forces revealed a need for the cartridge to be held more securely in alignment in the feed way for the extractor to pull the cartridge from the links.

This stop was intended to be staked to the existing front cartridge stop using two 3/32  notches  (only the top one is visible on the top view of the part.) 


B7162248 Revision 5 (10-9-52)  shows Revision 3 (6-13-51) adding a "finger" to the right rear of the stop. Revision 4 (2-28-52 adding a note about casting the part and revision 5 adding the casting drawing number .

Originally the M1917 and its derivative designs used only fabric belts.  The M1 metallic links were introduced in 1931, however, probably as a steel/machine time conservation measure, their use was restricted to aircraft ammunition until very late in WWII.

The original M1917 used a spring lock type hinge pin that was secured into a slot cut into back of the trunnion the top cover had no hold open feature. This spring pin arrangement was similar to the spring style pivot pin.  This evolved into a simple pin with a knurled head and a cotter pin retainer on the M1919A2 and very early M1919A4's.

In 1938 the spring loaded fixed/movable plates with the shoulder bolt/castle nut/cotter pin cover hold open device was introduced. 


Everything was just dandy until the metallic link ammunition for ground weapons became more prevalent.  Apparently reports about stoppages from links jamming on the fixed plate where it rested on the feed way came to the attention of the Ordnance establishment. 

This brought about the usual reaction, testing and the eventual redesign of the short round stop along with several several MWO's (Modification Work Order) being issued to the field forces for a fix.

This is a "cut and paste" job done long before computers existed which replaced the September,  1953 MWO with one dated September, 1954 which merely added the M1919A4E1 to the list of weapons to be modified.

Here's the illustration from the MWO that showed the small arms repairman what to do.



This wasn't the end of the design changes to the short round stop.

The stop on the left is the standard Revision 3 stop.  The one on the right, is the mystery part     Stock # 1005-6069673-A006 Drawing number 8413927.

It was manufactured, packed and preserved in 1959 and instead of the hole to slip over the existing front cartridge stop, it had a 8-32 tapped hole.  The screw shown is not the proper mounting screw, it's just there for illustrative purposes, and no screw was provided in the package which was sealed.  This stop was mounted using a screw likely staked to the chamfered stop hole in the right side plate.

We have not been able to locate the drawing, as by 1959 responsibilities for .30 caliber machine guns had been transferred from RIA to the Springfield Armory, and haven't figured if this part was intended as a maintenance fix to repair loose or missing front stops or served some other purpose.

As we have seen earlier, after September 1953 all .30 caliber air cooled BMG's, and the M1917A1 were supposed to have a short round stop installed.

This screw mounted stop is not the one called out for the plate assembly for the cast body, and it is not mentioned in the 1969 TM or the 1970 Depot Maintenance Work Requirements document.

This photo, courtesy of the Texas Military Forces Museum, Lisa Sharik, Registrar, shows A Buffalo Arms M1919A4  SN 279675 converted to M1919A4E1 by RIA with the screw mounted short round stop installed.  You can just see the end of the finger of the short round stop that extends over the fixed plate to keep links from jamming in the feed way peeking out. 

The head of the short round stop mounting screw appears to be staked to the right side plate.

 Also note the hole for the rivet that held on the bolt latch which has been removed at some point.

This cut of the casing group parts is from the SNL A-6 (May, 1941).  Note that this is the casing group parts, not just the casing assembly.  This SNL shows the different size orifices muzzle plugs for the front bearing for the M1 and M2 Ball ammunition and the slotted barrel jacket.


The original casing assembly drawing D35358 dated September 30, 1936 shows the M1919A4 in its original configuration with dovetail bottom plate, reinforcing stirrup and separate T&E bracket.

D35358 was redrawn on March 10, 1939 to show the D35392 bottom plate with the riveting flanges, integral T&E mounting holes and C45965 rear sight base.

March 10, 1939 seems to have considerable significance for the production model of the M1919A4 as many other parts and assemblies carry this same original drawing date.

The drawing shown above is Revision 8 which added the barrel jacket and screw to the casing assembly drawing along with the note to solder the jacket to the trunnion.

Ordnance couldn't seem to make their mind on whether the jacket should be shown on the casing assembly drawing or not.

Variously dated SNL's show different combinations of parts making up the casing group.

This cut from ORD 9 SNL A-6, the publication which replaced the previously mentioned SNL, dated April of 1947 shows a lot fewer parts in the casing group because some of the parts pictured in the previous photo, like the barrel, jacket, and bearing and booster plug now had groups of their own.

However, the parts of the casing assembly remained unchanged.

The combination of parts, top plate, bottom plate, left and right side plate assemblies, trunnion block assembly, the necessary attaching rivets and depending on which SNL (Standard Nomenclature List) you are looking at  the rear sight base and its attaching rivets and the breech lock cam and attaching screw are the component parts of the M1919 casing assembly.

None of the parts, with the exception of the breech cam lock and screw, barrel locking screw pawl pin, pawl and spring and top cover latch were available for field replacement yet the breech lock cam and screw were considered part of the casing assembly.  One more case of slight disconnect between official definition and actual usage

Ordnance considered the casing assembly to be "non-expendable" which is a round-about way to say that the casing assembly IS the weapon.

Nearly everything else is "parts".

The U.S. Treasury Department's Bureau 0f Alcohol, Tobacco, Firearms and Explosives (ATFE), however, considers only the right side plate as the "receiver" or the firearm, likely because that part has the identifying information including the serial number of both full auto and FFL 07 Dealer/Special Occupation Tax (SOT) license holder built semi-auto weapons.


                              CREDITS AND ACKNOWLEDGEMENTS


All of the Ordnance materials used in the preparation of this article through the courtesy and cooperation of the Rock Island Arsenal Museum Staff.                                                           

A special thanks to a special person Jodie Creen Wesemann, Museum Specialist-Registrar at the RIA Museum for her help, encouragement, and sharing the really odd finds.                                                                 
 A sincere thank you to the following:

Rollin Lofdahl, as always, came through with photos of the actual parts and good advice.

Matt Danker and Tom Chial  who also contributed to this article.

The members of the 1919a4.com forum for their encouragement.

Without Dolf Goldsmith and  Frank Iannamico's early works on the  on the Browning machine guns this would have been a whole lot harder to put together.

If you want to know the whole Browning story purchase their fine works.