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 TOP COVER LATCHES AND TOP PLATES FOR CALIBER .30 AIR COOLED BROWNING    GROUND TYPE MACHINE GUNS

 

Any discussion of the M1919 family of weapons always begins with a short history of weapons development.  The original M1919’s were designed from the M1917 water cooled model and used to provide machine gun armament for WWI tanks.  John M. Browning used the casing assembly of the M1917 and added an 18 inch barrel covered with a jacket with elongated cooling holes. 

The purpose of the jacket was to hold the "muzzle attachment"  and “muzzle plug” later known as a front barrel bearing and booster plug and provide support for the much heavier barrel required by the loss of efficiency of the water cooling system present on the M1917. 

The muzzle plug/booster provided additional gas pressure thrust on the front of the barrel to provide assistance to the recoil operated M1917 mechanism now laboring with a decidedly heaver group of recoiling parts.

The Armistice ending combat operations in WWI was signed before very many of these weapons were produced.

If the U.S. Army learned anything from combat experience in WWI it was that automatic weapons had changed the face of ground combat forever.

The Cavalry arm of the Army also discovered that to remain relevant they needed a way to increase combat power of mounted troops.

The Cavalry needed to add readily portable automatic weapon to their TO&E (Table of Organization and Equipment).

The Cavalry’s first attempt at this goal was to modify some Browning Machine Rifles to achieve this objective.  The result of this was the M1922.  The M1922 had a finned barrel to improve heat dissipation a barrel mounted bipod, and a butt stock rest. 

Some M1922’s had the sling swivels moved to the side of the weapon so it could be carried across the back of a mounted trooper.  This weapon was sometime referred to as Browning Machine Rifle like the original M1918.

While the M1922 gave mounted troops a readily portable automatic weapon it did nothing to alter the need for frequent magazine changes brought about by the parent weapon’s 20 round box magazine design which remained unchanged.   

In 1930 the Cavalry decided to try modifying some M1919 tank guns with the 18 inch barrel to see if these weapons would be more useful than the M1922.

The M1919 tank weapons came in two styles one having no sights at all and one having a tube sight mounted on the left side of the casing assembly.

The Cavalry test included jury rigging a front sight that was mounted on the jacket near the muzzle and drilling a hole parallel with the bore in the retracting knob for the top cover latch.  This made a crude sort of rear peep sight.

This rear sight was close enough for early tests, but when the Infantry got involved in 1931 it was decided to mount some sort of windage and elevation adjustable rear sighting device similar to the M1917’s.

Previous to WWI the Army had always mounted the rear sights of rifles on the barrels just ahead of the receiver. 

Wartime experience with the M1917 rifle, a U.S. Caliber.30 version of the  British P14 Enfield turned out to be an eye opening event, literally. 

This rifle, manufactured By Winchester, Remington and a Remington owned subsidiary Eddystone, so named because it was located in Eddystone, PA, was  adopted because Ordnance could not produce enough M1903 rifles.

The M1917 rifle, commonly called an "Enfield" had the rear sight mounted at the back of the receiver.

Combat evaluations convinced the Army that the closer the rear sight to the shooters eye the better the sight picture especially when using a peep sight.

An additional benefit of receiver mounted rear sights on rifles was that the sight radius was increased considerably. 

The M1917 rifle’s rear sight wasn’t adjustable for windage, but it proved to be a superior battle sight to the M1903’s finely made, windage adjustable, target style rear sight.

The P14/M1917 rifle sight, protecting ears and all, was adapted to the M1918 BAR which didn’t get a windage adjustable rear sight until its M1918A2 makeover. 

As things progressed on the modified tank gun testing on what would  later be known as the M1919A2, it was decided to mount the rear sight on the top cover latch placing the sight closer to the operators eye. This required removing the retracting knob for the latch.

No matter, the sight base would act as a handle to pull the top cover latch back. 

 

 Fig 1  Photo courtesy of Jon Moran 

This picture shows a M1919A2 commonly called the "Cavalry Model” with its adjustable rear sight mounted on the top cover latch.  The rear sight base serves as the retracting “handle” for the top cover latch.

 

Fig. 2

This assembly drawing, C64070, dated June 26, 1936 shows the rear sight base attached to the cover latch.  This arrangement was used  not only on the M1919A2 but the developmental models of the A4.

It is difficult to read but Revision 1 dated 6-15-37 added Major Items 51-83, the M1919A4 Fixed and 51-84 the M1919A4 Flexible to the "Drawing Pertains To" block in the upper right corner.

This means that this rear sight base arrangement was intended to be used on the M1919A4's until the adoption of the left side plate mounted sight base was implemented.

When the left side plate mounted rear sight base was adopted March 10, 1939, the latch mounted sight base "handle" disappeared, and a new method of retracting the cover latch had to be developed developed.

The period of time between official Ordnance Department  official adoption of the M1919A2, June, 1936 and the development of the M1919A4 overlap.  This goes a long way to explain why so few M1919A2’s were actually produced. 

Ordnance’s rebuild program, where M1917’s, M1919A2’s and anything else laying around were  converted to M1919A4’s  explains why so few, if any, M1919A2's survived in their original configuration.

 

Fig.3

This picture of a very early developmental M1919A4 Flexible dated February 25, 1936 showing the rear sight mounted on the cover latch.  Note the lack of a D35392 flanged bottom plate,  the slotted barrel jacket for the 24 inch barrel, no cover hold open device and a cotter pin style belt feed lever pivot.

 

Fig. 4

This photo dated the same day as Fig. 3 shows a Fixed version with a early style optical sight mounting that did not extend over the top of the cover latch.   This may be the "telescopic" sight bracket  that we have not been able locate the drawings for.

The rear sight is still mounted on the cover latch.  It is likely that this is the same weapon shown in Fig. 2 with the fixed style vertical buffer back plate installed, as that is the only difference between the M1919A4 Fixed and Flexible models. 

Figs. 3 and 4 are from a document titled “NOTES ON THE BROWNING TANK MACHINE GUN, CAL. .30 M1919, E2, AND BROWNING MACHINE GUN CAL. .30 M1919 A2 E3”

Courtesy of the Rock Island Arsenal Museum, Jodie Creen Wesemann.  These pictures to the best of my knowledge have never been previously published.

 

Fig. 5

As the design of the modified tank gun, now called the M1919A4, developed provisions for optical sights were retained.  In April of 1937 the RIA publication “Notes on the Browning Machine Gun Cal. .30 M1919A4” shows the new C45965 rear sight base mounted to the left side plate that would extend over the top cover latch and serve a mount for the iron sights at the same time retaining a mounting for optical sights.

This new style sight base combined the optical sight base with the latch mounted sight base.  

If you look at the left side of any production M1919A4 you will notice that the rear sight base has a cut parallel to the bore milled into the finished surface of the sight base along with 3 holes arranged in a triangular configuration.  These holes are tapped ¼ X 28 threads per inch.

The tapped holes and milled cut served as a mounting for optical sight bases.  These optical sight modifications never went  much beyond limited experiential use but they were never eliminated either.

Since the new sight base carried the rear sight and its raised protective enclosure there was no longer any way to retract the top cover latch.

To remedy this problem a handle was developed with a grasping protrusion on the right side that was to be riveted to the top of the existing top cover latches to facilitate pulling back the latch.

 Fig 5A

This is the original B150944 latch handle drawing.  Note that it has three mounting holes and and a slightly different configuration.

This drawing has no authorizing signature and was intended to be used on the Flexible model.

It is likely this drawing was only used to produce prototype latches.

Fig. 6

Drawing B150944 was completely revised on March 10, 1939 and eliminated the "hump" on the left forward end of the latch and one of the rivet holes and realigned the two remaining holes.  This re-design also required a piece mark imprint that was removed by Revision 6, 6-18-42.

 

Fig 6A.

This drawing is the last version of the latch handle developed after the adoption of the C45965 rear sight base that extended over the top cover latch.

You will note that this drawing and the previous one are dated March 10, 1939 which is the same date that the C45965 side plate mounted sight base uses for an original drawing date.

There is also a note on this drawing indicating that this part is not required on the "alternative method of manufacture C93166 is used".

C93166 is the cast latch with the integral handle developed by Saginaw Steering Gear which will be covered later in this discussion.

Top cover latches for both the M1917 and the M1919’s used a flat spring that attached to the inside rear of the top of the latch to apply forward pressure keeping the latch over the rear of the top cover.

Depending on the time frame the forward end of the latch spring was either bent downward or had a “V” formed on the end.

This downward bend or “V” engaged a detent cut in the top plate and held the latch in the forward position keeping the top cover securely closed.

The dynamics of repetitive recoil forces require that the latch be held firmly forward otherwise the top cover could spring open during firing disabling the weapon.

New operators of the weapon invariably complain about the difficulty of retracting the latch.

Even with a well lubricated latch it’s usually a two handed operation

Like most other things in life there is a reason why things are the way they are, and why the latch is difficult to manipulate.

Fig 6A    Photo Courtesy of Rollin Lofdahl

Left side, top and right side view of a cover latch with riveted handle.  The bead of weld was likely applied by the Israelis to tighten the handle .

We have found no mention in any Ordnance publication of using welding on any of the caliber.30 Browning machine gun parts.

Fig. 7

This illustration shows drawing 51-10-8 the M1917 top plate with the two transverse milled cuts for the cover latch spring.

The left portion of the drawing shows the M1917 top cover latch with the hole for mounting the spring retaining stud.  This stud had a 1/8 inch diameter and the latch spring just slipped over the stud.  This drawing also has the latch knob hole and the knob itself.  Notes show that these parts are also required by "CL.51 DIV. 18" which is the M1919 Tank Gun the predecessor of the M1919A4.

Other than latch knob hole this latch and top plate are very similar to latches and plates used on the M1919A4.

Fig 7A  Photo courtesy of Matt Danker

This picture is of two M1917 Westinghouse manufactured top cover latches.

The upper latch has been Ordnance modified to the rivet on latch spring.

The bottom latch and spring has been owner modified  to resemble the original stud mounted latch spring.

This illustrates the dilemma of trying to replicate a design that was superseded over 70 years ago, one has to make or modify existing parts.

Fig. 7B

This is detail D from drawing 51-10-34 showing the original design of the latch spring as used on the M1917.  It has the 1/8 inch hole to slip over the stud riveted to the bottom of the cover latch. 

It has been reported that some M1917 latches with the stud mounted  springs have been observed with the stud peened over to hold the spring in place.

It is not known whether this is some field expedient method of attaching the spring developed by some armorer with a little imagination, or something ordered by the Ordnance Department.

Fig. 8

This is the letter prefix drawing  B110372  Revision 18  showing the redesigned latch spring with the ¼ inch hole that was used to rivet the spring to the cover latch.  This drawing was not dated September 30 1936 which is the date found on most M1919A4 production drawing probably because this part was designed to replace the earlier design spring that was adopted with the M1919A2. 

Note the “Drg. Pertains To”  area of the title block which lists the weapons this spring is to be used on.   The M1917A1 is listed.

The M1919A4 is listed twice because the Fixed (51-83) and Flexible (51-84) models have separate Major Item numbers.  The upper area of the drawing shows the "alternate" style of fabrication with the hollow V.

Fig.8A

This drawing produced by Saginaw Steering Gear dated 3-2-42 and hand lettered "B110372" by RIA is what caused the "alternate" design.  Saginaw, ever trying to improve the the weapon and cut cost and increase production, was on their game as usual.

When pulling rearward on the latch you are flattening out the spring.  This spring is made so that when the spring is flattened the forward edge of the latch clears the rear end of the top cover allowing the top cover to be raised. 

The back plate latch stop screw or the lug cast on the ArmaSteel version of the back plate prevents the operator from pulling the latch completely off the weapon.

“Bumping” the latch farther rearward with the back plate removed causes the free end of the spring to jump clear of the forward  transverse detent cut in the top plate and the latch moves rearward about 2 inches farther where the “V” on the end of the spring engages another, shallower, detent cut milled in the top plate.

This second cut is a sort of “safety catch” to prevent the latch from being pulled off the top plate in one motion. 

It is believed by this author that the “safety catch”  detent was to prevent the loss of the latch and/or spring on early versions of the latch assembly because the spring was not permanently attached to the latch, it had the 1/8 inch hole that slipped over a stud on the inside of the latch.  

The transition from the stud mounted spring to the riveted on version occurred after October 1, 1938 the original date of the A152467 latch spring rivet drawing.

The May 1941 Standard Nomenclature List for the M1919A2 and M1919A4 lists the latch spring as available in two styles, the 1/8 inch hole B17483 version for the A2 and 1/4 inch hole B110372 for the A4.

The early latch spring was available as a separate part until at least January 1944. 

By 1947 only the latch ASSEMBLIES were available as repair parts.  While the individual parts were listed, they had no stock numbers shown and could not be ordered as repair parts.

The primary reason for riveting the spring to the latch was, in my opinion, an attempt to “soldier proof” the weapon.

If the spring wasn’t lost removing the latch, sometimes during reassembly the spring would become disengaged from the stud jamming the latch on the top cover. 

Freeing the latch invariably broke the spring  or the mounting stud rendering the weapon useless unless someone held the latch forward while firing.

 

Fig. 9

This original drawing, D35393, from February 1938 shows the “safety catch” cut on the left end of the Section A-A view.

 

Fig 9-1

This photo is of a Saginaw cast top plate with the two transverse detent cuts.

Note the difference in the profile and depth of the "hold close" detent on the right and the "safety catch" detent on the left.

The small letters "AC" on the rear sight windage knob indicate that this knob was produced by the AC Spark Plug Division of GM.  The sight leaf itself is marked BA for Buffalo Arms Corporation.  Did AC supply parts to Buffalo Arms? 

Hard to tell, as this sight leaf is a reworked Israeli 7.62X51 NATO sight and who knows if the sight was assembled with the original knob  after modification .

Fig 9A

The machining operation for the "safety catch"  detent cut was deleted by Revision 9 dated August 27,1942, because with the latch spring now riveted to the latch, the problem of lost or broken springs was greatly reduced. 

The note in the upper left of the drawing now requires the front half of the latch to be carbon case hardened probably to prevent wear on the bottom of the plate and the area around the cut where the cocking lever engages the top plate during the recoil phase of the firing sequence.

Fig 9B  Photo courtesy of Rollin Lofdahl

This photo shows both sides of a milled top plate with both transverse detent cuts.

Note the wear area to the rear (left) of the where the cocking lever dragged on the plate during bolt recoil.

The inside of the plate is marked "B 99" the meaning of which is unknown. 

The Ordnance Department didn't require marking on any of the WWII era casing component parts other than the breech cam lock, and after 1-19-42 the bottom plate.

However, manufacturers were permitted to mark parts for their own purposes with Ordnance Department approval.

Buffalo Arms marked many of their parts, likely to identify the multitude of sub-contractors used to provide parts for their M1919A4 production line.

Photo courtesy of Carl B

Cast single groove top plate, note the pebbled surface in the in the cocking lever opening.  Saginaw's subsidiary Saginaw Malleable Iron is the likely producer  of this plate. 

Although we have not found the drawing mentioning the use of malleable iron castings this top plate was likely produced sometime after mid 1943.  The half of the flaming bomb stamp on the left side of the plate indicated that this was installed on a Saginaw produced weapon.

Many cast parts have symbols or alpha-numeric codes that were likely used to identify production the meaning of which is not known because the Ordnance Department kept no records of these manufacturers codes.

Fig 10

In early 1942 Saginaw developed the C93166 latch cast with an integral  handle which eliminated the riveted on handle. 

Cast parts are fairly easy to identify as the un-machined surfaces have a grainy or pebbled appearance.

This is but another example of Saginaw's ability to use the ArmaSteel casting process to reduce the number of an assembly's component parts, in this case from 6 parts on the Ordnance designed latch to 3 parts on the cast latch, saving production time for the parts no longer required, material and the time required to assemble the parts.

Fig 11

The original date on this Saginaw produced drawing with C93166 hand written on the face is illegible, however, the Revision A date is 10-10-42 which is pretty close to the original date of October 31, 1942  on the Ordnance drawing C93166. 

It is possible that Saginaw was producing these cast latches before these dates, but there is no way to know that.

Fig 12  C93166 Revision 4. 

This drawing is the Ordnance drawing of Saginaw's cast latch.  The note at right center indicates that this design is an "Alternative" design tor C64246, the machined latch, B150344 the handle, and A159791 the rivets to hold the handle on. 

The "Heat Treatment and Final Finish" block in the upper left corner of the drawing shows "flame hardening" the 7 degree angle on the lip of the latch that passes over the rear edge of the cover to hold it closed. 

Flame hardening for the cast latch replaces carbon case hardening of the latching lip on the machined C64246 latch, and is the standard method of heat treatment for cast parts.

Alternate sometimes called Alternative designs indicated that more than one design was approved, produced and used.  It is very possible that Saginaw was producing both type latches at the same time.

From this point in time it is difficult to state which manufactures other than Saginaw, the only known WWII producer of cast parts for the M1919's, were using the cast latch, and since the cast and machined latches were interchangeable there is no sure way to know how weapons produced by RIA or Buffalo Arms left the factory.

Eventually the latch assemblies using the flat spring was replaced by a Saginaw Steering Gear designed latch featuring a spring loaded plunger to hold the top cover latched and another plunger at the rear to dismount the back plate assembly.

This plunger style latch was originally designed for the M1919A6 variant but proved so popular that it became the standard for all models.

Fig 13

This Saginaw produced drawing is dated 8-12-43 and shows the detail of the spring loaded plunger and the plug that kept the  top cover latched.

As of now we have not discovered exactly what prompted this development.  The date of this drawing is about two weeks after the M1919A6 parts specific drawing are dated.

Since the A6 was originally used  without a tripod in the prone position this may have been an attempt to solve some concerns regarding the difficulty of retracting the latch due to the butt stock or it could have been developed because of complaints about the latch being difficult to manipulate.

 Fig 14

This is the original B7106949 plunger style latch assembly drawing, dated October 7, 1943, showing that this latch is an experimental part developed for the M1919A6. 

Note that the Submitted and Approved signature areas are blank meaning that this was not yet a part approved for production.

 Fig 15

Revision 1 to B7106949 dated 3-9-44 has the authorizing signatures and would indicate that this part was in production at least by that date.

Originally this part was intended for the M1919A6 only.

However, Revision 3 dated 6-12-45 added the M1917A1, the M1919A4 Fixed and Flexible and the M1919A5 Fixed tank gun to the "Drg. Pertains To" block.

By June 12, 1945 the war in Europe had been over for a month.

 

Fig 15A  Photo courtesy of Rollin Lofdahl

Right side view of the plunger style latch assembly.

Fig 15B  Photo courtesy of Rollin Lofdahl

Bottom view of plunger style latch assembly.

The way this assembly functioned was the vertical plunger, the round part shown in Fig 15B engaged the "hold closed" detent cut in the top plate it was spring loaded by the plug and the compressed spring held by the horizontal plunger which was retained by the pin.

To remove the back plate the horizontal plunger was pushed forward to clear the top edge of the back plate.

No more prying the latch forward with a screw driver wedged between the back of the latch and and the back plate.

The note on the bottom left of the drawing in Fig 15 indicates that C64247 the latch assembly for the A4's and A5 and C64280 the latch assembly for the M1917A1 were no longer to be produced.

The older style latches remained in the supply pipeline and as late as the April 1947 SNL still showed all four types.

The C64070 assembly with the sight base mounted on latch had no associated stock number meaning it could no longer be ordered.

The C64247 assembly which was both the rivet on handle and the alternate cast style were classed as (usable) but the stock number was hand lined out in my copy of the SNL.

This left the the B7106949 plunger style being the preferred assembly, sort of.

The Army was not about to throw away perfectly good parts just because it made the latch easier to manipulate.

 Fig 16

This cut is from TB ORD 366  the Overhaul and Rebuild Standards For Small Arms Material dated April,1949.

It pretty much explains the  required procedure in subparagraph (g) The A4 and A5's could have either latch, the M1917A1 could have either latch, and the M1919A6 got the plunger style latch period.

Fast forward to 1969 and 1970 the TM9-1005-212-25 dated May 1969 shows only the plunger style latch for the A4 and A6, the M37 used an entirely top cover.

Depot Maintenance Work Requirements published in May, 1970 makes no mention of the anything but the plunger style.

Like most things connected with the Ordnance Department, the M1919's and WWII there is always a mystery.

Fig 17  Courtesy of the 90th Infantry Division Association

This is a picture from TM 9-206, the original M1919A6 Technical Manual published in September, 1943.

The top cover latch shown does not resemble any thing we have seen previously.

It appears to be some sort of flat spring that holds the top cover down.

Another anomaly in this picture is the use of the flat bottomed grip, sometimes called the "short handle", C121054 cast back plate normally used on the M1917A1.

This style grip lacks the cut out and spring clip used to latch up the T & E mechanism when moving a weapon off the M2 tripod.

This picture was coded RA PD 79900 we believe this to be Raritan Arsenal Publications Department #79900.

The Raritan Arsenal was located in  Middlesex County, NJ and among other things seems to have been the Ordnance Departments WWII publishing house. 

This facility closed in 1963.

Many Ordnance publications are coded RA until about 1947 when the U.S. Government Printing Office resumed publishing Ordnance materials.

 

                                 CREDITS AND ACKNOWLEDGEMENTS

 

Unless otherwise noted, all of the Ordnance Department materials used in this article were provided by the Rock Island Arsenal Museum.

A sincere thanks to the Museum staff and especially Jodie Creen Wesemann for their help and assistance.

Without the cooperation of the Museum none of these our articles would be possible.

As usual, Rollin Lofdahl and Matt D contributed photos of the real thing which adds to the impact of the drawings.

 

Thanks to all who have contributed photos and provided encouragement.