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                             Boosters and Flash Hiders

The story of boosters goes all the way back to John Moses Browning's adaption of the Model of 1917 water cooled machine gun to the 18 inch barreled air cooled M1919 Tank Machine Gun needed for arming U.S. made tanks at the close of WWI.

Apparently the Ordnance Department considered a water cooled weapon wholly unsatisfactory for mounting in the close quarters of the period's tanks. 

Besides being too bulky there was the problem of the water jacket being pierced by bullets or shrapnel rendering the weapon useless.

During the initial design phase several problems needed to be a addressed. All of them having to do more or less with the dissipation of barrel heat.

The first and most serious was the loss of water cooling efficiency of the M1917 barrel.

Browning had already designed air cooled machine guns for aircraft use however ground use weapons presented a somewhat different set of problems.

The aircraft guns were only used while actually flying and the large volume of air passing the barrel tended to mitigate the loss of the water jacket cooling efficiency and to help dissipate the barrel heat.

The Tank  Gun did not have this advantage.

The M1917 was a purely recoil operated weapon, that is a portion of the forces produced by cartridge ignition caused the barrel, barrel extension and bolt to recoil together until the projectile left the barrel and the 50,000 psi chamber pressure dropped to near normal levels at which time the bolt was unlocked.

The bolt continued to the rear under recoil while performing other functions such as extracting a fresh cartridge from the feed belt and the expended cartridge from the chamber.

Some of this recoil energy was stored in the driving spring contained in the bolt and as the bolt reached the rearward end of its stroke it was driven forward by the stored energy of the driving spring closing and locking the bolt and readying the weapon for subsequent shots.

The M1917's 24 inch barrel weighed 3 lbs the 18 inch Tank Guns barrel weighed about 5.5 lbs because of its larger diameter necessary for better heat dissipation.  This increased the weight of the recoiling parts considerably.

Since the recoiling parts became quite a bit heavier and the energy produced by the cartridge remained the same, additional energy to reliably operate weapon had to come from somewhere. 

It wasn't much of a leap to modify the muzzle attachment used on the M1918 Aircraft weapon who's principal purpose was to support the end of the barrel and speed up the rate of fire.

Redesigning the aircraft style muzzle device and opening up the orifice for the projectile to pass out, the propellant combustion gasses trapped during the very short time when the projectile entered and left the booster chamber considerable rearward force could be applied to the front of the barrel. 

By varying the size of the opening more or less force could be applied.


Drawing 51-18-5 courtesy of the RIA Museum, Jodie Creen Wesemann

The upper drawing shows several of the parts used in the redesign of the M1917 water cooled machine gun to the air cooled M1919 Tank Machine Gun. 

The lower picture is a close-up of the muzzle attachment and plug. 

On June 1,1931 the muzzle attachment became the front barrel bearing drawing B134052 and muzzle attachment plug became the front barrel bearing plug drawing A13254 for the M1919 Tank Machine Gun.

These parts that provided "boost" to the recoil dynamics were known as the muzzle attachment and muzzle attachment plug and during the M1919A4 development officially became the front barrel bearing and the front barrel bearing plug.

Today these parts are commonly called booster/bearing and booster plug.

 Photo courtesy of amish-bob

This photo shows an original New England Westinghouse M1919 Tank Machine Gun booster and plug installed on the slotted barrel jacket.  The tank guns are extremely rare because only between 1800 and 2600 were actually completed and the majority of these weapons were converted to M1919A2 configuration then to M1919A4 configuration in the late 1930's

Note that there are no locking bands between the barrel jacket and the booster and the booster and plug.  The seam between the booster and the jacket is very hard to distinguish.


Photo courtesy of amish-bob

The orifice on this booster plug is .872 inches for the M1906 cartridge.

Opening size varied considerably during the development years of the M1919 air cooled ground guns because of changes in the design of the .30 caliber cartridge and attempts to increase the rate of fire.

The slots in the plug and the notches in the bearing are used to remove the parts for cleaning using either the M6 wrench or a socket type wrench.

Photo courtesy of the RIA Museum, Jodie Creen Wesemann. 

This is an early developmental version of what would become the M1919A4 mounted on the 48 lb M1917A1 tripod. 

In place of the usual tank gun booster this version has a  "T24 Stabilizer" designed by Springfield Armory and appearing on drawing SA9978 it was equipped with a .625 orifice.  which produced a firing rate of 425 rounds per minute

Research has not as yet turned up much information on the stabilizer, however, Ordnance Committee Meeting minutes suggest that there was some concern about recoil forces acting on a new light weight tripod the M2, and the stabilizer was likely an attempt to address those concerns while providing the "boost" feature necessary for reliability.  The stabilizer is likely is a sort of recoil check/muzzle brake combined with a booster.

Photo courtesy of RIA Museum, Jodie Creen Wesemann

By 1937 the stabilizer had gone by the wayside and the prototype conversion of the existing M1917's into M1919A4's, like the one pictured above, had reverted back to the tank gun style booster and plug. 

One thing that complicates the study of boosters is the number of things going on in the various branches of the Army all at the same time and often at cross purposes.

The standard service round during WWI, the U.S. Caliber .30 Ball Cartridge, Model of 1906, featuring a 150 grain pointed projectile at 2640 fps was replaced in early 1926 by a new service cartridge equipped with a 174 grain boat tail projectile at 2600 fps. 

This change increased the effective range of service ammunition from about 2000 yards to about 3000 yards.

The Army's system of nomenclature changed in 1926 and when this new cartridge was described under the latest naming convention it was known as U.S. Caliber .30, Ball Cartridge, M1. 

Between 1926 and about 1936 the stock of almost 2 billion rounds of the original 150 grain M1906 WWI ammunition, now being used for training, was slowly being exhausted or found unfit for use.

As more of the M1 Ball ammunition made its way to into the supply system the Ordnance Department began receiving reports that the M1 Ball cartridge exceeded the safety limits of some rifle ranges.

The range safety issue combined with the 1936 adoption of the M1 gas operated rifle using M1 Ball ammunition which reportedly caused malfunctions led to the rethinking of the whole service cartridge issue.

This rethinking resulted in the 1936 resurrection of the 150 grain M1906 load. 

This cartridge, nearly identical to the WWI version, because of the previously noted changes in the nomenclature system became known as the M2 Ball and featured a 152 grain flat based pointed projectile.

The nominal 2 grain increase in projectile weight was the result of changes to the composition of the lead core.

Compounding this was the Army Air Corps and the Navy's desire to retain the M1 Ball cartridge for aircraft use because of it's superior performance and the logistical absurdity of two kinds of ammunition in the supply system and trying to keep the users supplied with proper ammunition that their weapons sights were calibrated for.

Eventually the Air Corps decided that they would use only .50 caliber weapons on aircraft which removed one set of objections to the M2 Ball round and the logisticians won the day and on January 12, 1940 the M2 Ball cartridge was declared the Ordnance Standard.

Meanwhile back at the ranch, in early 1936 RIA was going through an exercise trying to adopt the prototype M1919A4's to the M1 Ball cartridge.


Drawing courtesy of the RIA Museum, Jodie Creen Wesemann

As is evident from this drawing the orifice size was increased from the original .872 for the M1906 cartridge used in the 18 inch barreled tank guns and M1919A2's to .921 to compensate for the increase in the 24 inch M1919A4 barrel's weight to 7.5 lbs and the more powerful M1 Ball round.

May 1938 brought some additional experimentation this time it was an attempt to increase the firing rate from 425-450 to 500- 600 rounds per minute.


Courtesy of RIA Museum, Jodie Creen Wesemann

Cut from document "Notes on Browning Machine Gun Caliber .30 M1919A4 MODIFIED" prepared by RIA April, 1938

This increase in the rate of fire was to be accomplished by shrinking the booster plug orifice for the M1 Ball cartridge from .921 to .617 and using a heavier driving spring, however this was based on the more powerful M1 Ball cartridge.  The best they did was 500 rounds per minute.

Finally cooler heads prevailed and the project was abandoned.


Courtesy of RIA Museum, Jodie Creen Wesemann

By February, 1939 the orifice for the M1 Ball round was reduced to .870 and a new drawing B147157A Revision 3 (6-28-41) with a .718  orifice for the M1906 Ball and the M2 Ball round was produced.  Note the marking for the .30 M1 round on the B147157 drawing.

Courtesy of RIA Museum, Jodie Creen Wesemann

Apparently the B147157A Revision 3 drawing was intended to provide a plug of the proper size to accommodate both the M1906 and the M2 Ball cartridges and now that the dust had settled on the increasing the rate of fire project the engineers at RIA compromised on the new orifice diameter of .718.

Rollin Lofdahl photo

Many of the plugs with the .718 orifice, which remained the standard even in the one piece bearing designs, are marked with the dimension. 


 amish-bob photo

This is a rather rare variant, a plug marked for both the M1906 and its virtual clone the M2 Ball cartridge.  It has an .810 orifice.  We are still looking for the drawing indicating this marking and orifice size.

A few have been observed with flaming bomb markings and are generally thought to be of Saginaw Steering Gear manufacture.  RIA marked plugs have also  been observed.

Courtesy of RIA Museum, Jodie Creen Wesemann

This is the original drawing for the M1919A4 Fixed and Flexible models front barrel bearing. Note the lack of cuts for the locking bands and the absence of staking points and the requirement to piece mark the part.

Courtesy of RIA Museum, Jodie Creen Wesemann

Apparently, in 1939, during testing of the new M1919A4 another problem cropped up.  The plug and/or front barrel bearing would vibrate loose during extended firing.

To solve this problem the joint between the plug and bearing and the bearing and barrel jacket have a sheet metal ring installed that when compressed by tightening the components applied friction the parts which would then be staked in place.

The drawing of the front barrel bearing shown above added by Revision 2 (May 2,1939)   cuts to accommodate the bands, commonly called  lock rings, along with a 1/8 inch drilled hole (sections A-C and B-B) to provide a staking point for the band.

Note the May 15, 1942 addition of the M1919A5 in the "DRG. PERTAINS TO" block.

 Author's photo


This photo shows the B147157 BEARING, barrel, front with the two bands and bearing plug. This design was issued throughout WWII even after being replaced by the one piece designs.

The band to the left shows proper positioning for staking, at the right you can see the cut made to accommodate the smaller front band and the 1/8 inch drilled hole for the staking point. 

The muzzle plug shown in the foreground is an Ohio Ordnance Works reproduction with  much superior machining and finish compared to the WWII production bearing.

Note the faint stamped "flaming bomb" to the left and the numeral 1 at the far right of the bearing.

The "flaming bomb" Ordnance symbol is common on Saginaw produced parts and on some bearings produced at RIA.  The meaning of the "1" is not known but is likely a production code.

Some front barrel bearings have been noted with RIA and occasionally a drawing number/ piece mark imprint. 

These piece marked bearings were likely produced before October 15, 1941 when Revision 3 to the bearing drawing removed the marking requirement.

Tim Gaine Photo

Buffalo Arms (BA) marked boosters have also been observed, however, the ones seen so far lack the piece mark imprint.

Front barrel bearings, both the two piece and the later one piece and later still the combination bearing/booster/flash hider were packaged with the bands, and the muzzle plugs were packed with the smaller band.

Bands were not intended to be reused and could be ordered as a replacement part.


Courtesy of RIA Museum, Jodie Creen Wesemann

This is the original drawing dated July 18, 1942 of the tapered one piece front barrel bearing often referred to as the "A5 booster".

The M1919A5 was an outgrowth of a program that modified M1919A4 Fixed type weapons to be used in M22 and M23 combination mounts in the M2A4 and M3A1 Stewart light tank.  The modified M1919A4 fixed weapons became M1919A5 Major Item 51-114 in May, 1942.

As is noted on this drawing and on the previous drawings of the two piece style that either type could be used on either weapon.

There is no official "A5" booster.

Published pictures of a M1919A5 assembly line at RIA show A5's with non tapered bearings.

The reason for the tapered design is usually thought to make it easier to insert the muzzle into either a combination or ball mounting in a tank.

Photo courtesy of Rollin Lofdahl

The B221301 bearing with tapered exterior profile.  The drawings for this style were maintained until February 1945 until superseded by the straight sided version. 

In any event a new design one piece bearing appeared in March 1943.


Courtesy RIA Museum, Jodie Creen Wesemann

This design started out as an alternate method of manufacture for the tapered style one piece bearing. 

While no evidence has yet surfaced, this looks like an innovation developed by Saginaw Steering Gear who's engineers were always on the lookout for ways to speed up production and reduce machine time.

This design eliminated the exterior taper and simplified the machining of the interior by eliminating the angle cuts. 

Both the tapered and straight sided versions piece used the now standard .718 orifice.

Courtesy RIA Museum, Jodie Creen Wesemann

In February, 1945 the original tapered bearing design was superseded by the straight sided version, but the original interior contour with the angled cuts was retained and the rounded style interior was also authorized as the alternative design.

Rollin Lofdahl photo.

The upper photo shows the post-July 1943 straight sided one piece bearing and the lower picture the same part in its original packaging. 

While the label lists the M1919A4, the Standard Nomenclature List A-6, List of All Parts, dated September, 1943 shows the item stock number A006-01-00101 as "used on guns of present manufacture (M1919A4)  (M1919A5)"


Cut from Depot Maintenance Work Requirements 9-1005-12 (1970)

Courtesy RIA Museum, Jodie Creen Wesemann

The bottom bearing illustration which we have not been able to locate the drawing for.  It appears to be a refinement of the B221301 Revision 8 (May, 1948) and reintroduced an exterior taper, added a chrome plated interior and retained both interior configurations.

The taper is likely for the same reason as the original one piece bearing, to aid in inserting the weapon into a mounting.  The M37 was developed primarily for use in armored vehicles.

The author has not seen this configuration in the flesh.

One piece bearings offered several advantages, they eliminated two of the parts, the plug and band of the two piece bearing and plug assembly and eliminated many machining operations involved in making the plug and cutting the front of the bearing for threads and the band.

With every advantage comes a downside.  The two piece bearing/plug was easier to clean the carbon deposits out of because it could be disassembled.


Tim Gaine Photo

Ordnance developed a tool called "carbon removing reamer assembly" drawing 7106460.

The one or two piece bearing was screwed on to this device after removing it from the barrel jacket. 

Turning the attached crank while holding the body of the tool scraped out the carbon deposits.

From the drawing number it appears to have been developed in late 1943 or early 1944.

This tool was likely used by Ordnance troops working in mobile shops or depots.

Both the two piece and the one piece bearings sometimes required cleaning in the field and tools were needed to assist in disassembling the bearings.

The two basic tools developed were the M6 combination wrench C68334 and a socket wrench B147277.


Author's photo

The inside of the socket wrench is shown on the top right and the M6 combination wrench at the bottom.  Note the rectangular cuts in both the plug and the muzzle end of the bearing and the elongated hole in the M6 wrench.


Author's photo

The edge of the M6 wrench fits into the cuts on both the plug and the bearing  giving a good grip and some mechanical advantage.

Author's photo.

The elongated hole on the M6 wrench should fit over the socket.  The socket also had wrench flats for using an adjustable wrench and a hole that a screwdriver or rod could be inserted into to help in removing the plug or bearing.

Cut from TM 9-206 September, 1943 courtesy of 90th Infantry Division Association

When the original production M1919A6 appeared on the scene in September 1943 it had no gas assist/boost feature.  Instead, the designers, trying effect a front barrel changing feature, lightened the barrel by making changes to its contour, shortened the barrel jacket and developed a front barrel bearing that also supported the A6 bipod.

The muzzle end of the A6 barrel had wrench flats that protruded from the end of the front barrel bearing which fit the oblong hole in the M6 combination wrench.

The M6 wrench could be used to unscrew a hot barrel from the barrel extension from the muzzle end and replace it without field stripping the weapon.

It was thought that the lighter barrel would not require the gas assist/boost.

The A6 made its combat debut in the Salerno campaign in the fall of 1943 followed by the Anzio invasion in early 1944.

Things did not go well. 

The lack of a boost feature while apparently not causing problems during testing led to complaints from the combat users regarding weapon reliability especially with the muzzle elevated.

 Cut from ORD 9 SNL A-6 April 1947 Courtesy RIA Museum Jodie Creen Wesemann

The combat reliability issues led to a redesign of the front barrel bearing and the addition of a cap style booster retained by a "U" shaped spring clip along with a slightly shorter barrel jacket.

This redesign allowed the front barrel changing feature to be retained and for the moment solved the reliability issues.

By late spring 1944 all of the redesigned parts necessary to correct the earlier noted deficiencies in the A6's reliability were in production.

We have not as yet discovered any Modification Work Orders or Technical Bulletins that indicated how the A6's already in stores or in the field would be modified.

There are a number of official photos taken overseas dating from June 1944 showing the modified A6 with the cap style booster so the modifications must have been a high priority item. 


Photo courtesy BMG Parts Inc.

The cap style booster for the A6 which used a .812 orifice remained in service through the Korean War even though RIA had completed production drawings for a combination booster/flash hider the M7, for the M1919A6 by July of 1945 and had commenced production in 1949.

Besides the common one piece bearings there are a few not so common ones.

 Rollin Lofdahl photo

This is an RIA produced one piece bearing for the U.S. Navy's MK 21 MOD 0 variant of the M1919A4 which was modified to use 7.62X51 NATO ammunition in M13 links to arm river patrol craft in Viet Nam.  The orifice measures .525 inches for the slightly less powerful ammunition being used.

  Photo courtesy of amish-bob

This bearing was likely produced by Springfield Armory for the M37 after they assumed engineering responsibilities for the .30 caliber Brownings in July, 1957.

By this late date all of the M1919A4's were supposed to be equipped with M6 flash hider assemblies.

The drawing/part number is unknown as it was unpackaged and not imprinted with a part number it has a slightly more rounded profile and the interior is chrome plated.

The orifice is the standard .718 diameter.

Rollin Lofdahl photo

The Israeli Defense Force received thousands of M1919A4's as military assistance items in the late 1950's and they promptly converted them to 7.62X51 NATO caliber. 

As with the MK21 MOD 0 bearing shown above the .718 orifice for the more powerful M2 Ball ammo did not provide enough "boost" for reliable operation. 

The IDF solved the problem by boring out the orifice and installing a bushing to reduce the orifice to about .532. 

These are usually marked "13.5mm"  in Hebrew notation and the IDF "upside down U" symbol which served the IDF in the same fashion at the Ordnance flaming bomb property mark.

The IDF also had  some M1919A4's converted to 7.92X57 aka 8mm Mauser.  These weapons required yet another booster orifice size and the Israelis decided that 15 mm or about .590 inches would serve their needs best.

amish-bob photo

This photo shows the standard 7.62X51 NATO muzzle plug on the far left and two differently marked 15 mm plugs intended for 7.92X57 chambered weapons.



Photo courtesy of Carl the Jackal

On the left is a two piece booster modified for Canadian Forces use on the C1/C5A1.  The booster plug orifice was drilled out and sleeved down to .625 and the band was blind pinned to the bearing in three places to prevent removal and possible replacement with a standard .30 caliber plug.  The pinning was usually done by field ordnance personnel. 

The one piece bearing on the right was also sleeved down to .625.  The C1 and C5A1 variants were modified M1919A4's fielded by Canada using 7.62X51 NATO ammunition in M13 "push through" style links also used in the M60 GP machine gun.

Photo courtesy of Carl the Jackal


Close up of the Canadian modified booster plug which started life as a US produced Caliber .30 with the .718 DIA. marking .  The sleeving modification is very evident.



The subject of "flash hiders" is much misunderstood.  There is no way to completely hide the muzzle flash of any weapon using common propellants, especially if the muzzle is pointed at you.   Just because it couldn't be done doesn't mean the Ordnance Department didn't try.

Smokeless propellants operate by combustion producing large volumes of gasses rapidly raising  pressure inside the cartridge case until the projectile is expelled from the cartridge case and barrel of the weapon.

Muzzle flash is the result of the incomplete burning of the propellant while the projectile is in the bore.  These hot gasses escape from the muzzle behind the projectile, combine with the oxygen in the air, and ignite.  In sunlight it is hard to see this flame, in low light conditions this ball of fire is quite impressive even from the pipsqueak .22 Caliber rim fire cartridge. 

M1919A4 night firing shows burning gasses escaping to the rear of the front barrel bearing/booster and illuminating the holes in the barrel jacket along with some sparks flying out the muzzle.  It is a real attention getter to say the least.  Add a few tracer rounds and you have a better light show than a Ted Nugent rock concert.

Military use of modern "smokeless" propellants date from about 1885 when the French army adopted the 8mm Lebel rifle and its accompanying cartridge.  These early propellants are sometimes called "semi-smokeless", they smoked less than the black powder previous used but were not nearly as clean burning as today's propellants.

Once the French let the cat out of the bag everybody in or near Europe got interested in the concept of small bore, magazine fed, smokeless propellant rifles. 

Germany, France's latest worst enemy, having replaced the British after six or seven hundred years, got really interested in propellant development and with typical Prussian interest in anything associated with war making started on their own program. By 1888 their chemical industry developed relatively efficient and low flash small arms propellants.

Here in the U.S. we were still busy chasing/being chased around what was left of the the western frontier by the various tribes/bands of plains Indians.  Apparently, it was felt that the .45-70 black powder round in the trapdoor Springfield rifle dating from 1873 would do just fine.  

By 1892 the U.S. had developed it's own small bore cartridge a rimmed bottlenecked affair looking suspiciously like the .303 British service round but with a slightly smaller diameter projectile.  The development of the .30 Caliber U.S. Army aka .30-40 Krag cartridge was complete with buying foreign made propellants.

While the Frankford Arsenal had the ability to produce primers, cartridge cases and projectiles and reloading kits for cartridges the Ordnance Department did not have the ability to mass produce propellants of any kind.

While the Krag rifle and carbine was several orders of magnitude better than the Trapdoor Springfield it was obsolete when adopted.  A 220 grain round nose projectile at 1600 feet per second just didn't cut it. The Army and Chief of Ordnance Crozier, got a tune up from a Spanish-American War vet and Rough Rider, and today who would be called in the liberal press "a gun nut",  President Teddy Roosevelt, who it is said, as President rode a horse at a gallop, unaccompanied, through Rock Creek Park shooting at rocks just for the Hell of it.

Boy,  the author misses him. 

Teddy wanted a Mauser rifle but in .30 Caliber, rather than the 7X57mm Spanish weapons he faced on Kettle Hill.  He got  the Model of 1903 "Springfield" rifle, and in 1906 a spitzer projectile that even today can reach out and touch you at 1000 yards with good ammo and the hands of a skilled marksman.  The Laws of Physics have not changed with the advent of smart phones.   

The primary purpose of flash hiders is to protect the night vision of the operator of the weapon its secondary purpose is to limit the field of view or intensity of the muzzle flash to everybody else.  It is highly unlikely that using propellants that operate by combustion that this problem will ever be solved to the satisfaction of everybody involved.

WWI, the first mass use of automatic weapons combined with siege warfare and bloodletting on a previously unimaginable scale highlighted the problem of muzzle flash from weapons.

Since the machine guns of the time were fired from heavy and very stable mounts and difficult to relocate a couple of long bursts invited counter-battery fire from field artillery making machine gunners something less than popular with the other trench bound troops.

Night time made the problem worse.  U. S. Troops took to draping wet empty burlap sand bags over the front of the weapons while firing at night in an attempt to reduce flash signature.

However, one had to change the bags at short intervals because after a few bursts they dried out and caught fire negating the flash hiding.  Some weapons like the German Maxims had a rudimentary flash hider that deflected the flash off to the sides of the muzzle through a series of ports.  This device also acted as a booster.  The Browning Model of 1917 had nothing of the sort and during low-light conditions operated at a disadvantage wet burlap bags not withstanding.

Somewhere along the line something described as a "night firing box" was developed. From the very sketchy details gleaned from the Ordnance Committee Meeting minutes this device apparently enclosed the machine gun in some fashion. Whatever it was it was not well liked.

On November 4, 1919, less than a year after the Armistice, the Ordnance Committee read into the record a letter from the Adjutant  General  addressed to Chief of Ordnance Major General Clarence C. Williams containing a long list of  suggested changes prepared by "our best machine gun officers". Topping the list was a request that something be done about the "night firing box" as it was thought to be "too elaborate and bulky" a short way down the list was a request for a flash hider and "A real smokeless and, if possible, a flashless powder is needed.  Our powder is far from flashless and disclosed the position of the guns at once."

The machine gunners weren't the only complainers and the Adjutant General's letter stirred up a beehive of activity on the flash hider front. Instead of concentrating on a single objective the Ordnance Committee and its various sub-committees began moving off in several directions trying to solve flash signature, muzzle jump, and recoil problems in various small arms all at the same time.

The Ordnance Committee's first order of business was to circulate the AG's letter to the various Ordnance Bureaus and Departments to see if any projects or developments concerning the complaints were in the works. 

It didn't take long to get an answer from the Springfield Armory.  They reported back on November 14 that they had already tested four different designs of the "Thomas Flash Hider "and all had proved unsatisfactory".  Springfield further stated that "In view of the unfavorable results obtained the tests, it is recommended that there be no further tests of this design of flash hider.  The Small Arms Sub-Committee concurred.

The May 5, 1920 Ordnance Committee meeting shed further light on the nature of the Thomas flash hider.  Thomas was a Captain in the Ordnance Corps and his flash hider not only "did not satisfactorily  obscure the flash" but "does not remain in place on the gun".   Flash hider development for the Model of 1917 BMG proceeded  at the usual glacial pace of the cash strapped peacetime U.S. Army.  The Springfield Armory continued to tinker with the "German" (Maxim) flash hider and considered other designs including one discussed as Item 2368 at the Ordnance committee meeting on September 15, 1922. 

Captain A. F. Gilmore of the Coast Artillery Corps submitted another flash hider design, somewhat similar to the Thomas, deemed to be "very efficient, though composed of many parts, and somewhat expensive to make, at least in the experimental stages" however, it also got shot of the muzzle after a "considerable amount of firing has been done".   The Sub-Committee on Infantry Armament report goes on to say that Springfield Armory had perfected a new style of flash hider that would be submitted to the using services for testing in the near future.

 By November 1922 approval was obtained for “one modified German flash hider” together with one of the Springfield Armory type to be submitted to the Infantry Board for testing.

The March 23, 1923 Committee meeting reviewed as Item 2774 the report of the flash hider testing from Aberdeen Proving Ground.  The conclusion of the proof officer, approved by the Commanding Officer was that the modified German flash hider “gave the best results, and was superior in every way.”  However, in a dazzling display of fancy foot work and buck passing, Aberdeen stated that “in view of the fact that the flash hider designed by the Springfield Armory gave fairly good results and in consideration of a statement from Manufacturing Services (Springfield Armory) to the effect that the cost of Springfield Armory type would be considerably less than the German type, it is believed that both flash hiders should be tested by the Infantry…”

By the July 27, 1923 meeting of the Committee the story had changed somewhat.  Item 3149 considered at this meeting stated in part, “These flash hiders have been tested at Aberdeen Proving Ground and by the Infantry Board with results that show very little difference in efficiency, while both are very good.”  The Infantry Board recommended adoption of the Springfield Armory type apparently based on cost and the fact that it was an indigenous design never minding the fact that the “German” type was "superior in every way" four months earlier.

The December 27, 1923 Ordnance committee meeting took up Item 3462 which was specification No.52-5-12 the flash hider for the Model of 1917 BMG.  This specification was approved and result was the M1923 flash hider.  The shooting off of the flash hider problem was solved by removing the muzzle gland from the end cap of the water jacket and screwing in the flash hider. 


   RIA Museum Jodie Creen Wesemann


The M1923 flash hider resembled previous designs except that it had vent holes in the exterior and functioned by allowing the unburned combustion gasses from the propellant to swirl around a series of baffle holes between the chamber that the projectile passed through called the inner spool and a helically wound coil spring between the spool and outer casing finally venting into the air.  This allowed cooling and gradual mixing of the residual combustible gas with oxygen in the air.  The flash hider was piece marked with the drawing number D1804 and underwent a proof test signified by the “P” stamped on the rear.  It appears that all of the M1923 flash hiders were produced at Springfield Armory until RIA became the Ordnance primary engineering support and production facility for the .30 caliber BMG’s about 1936.  Although not often seen actually on the weapon, the M1923 was a standard accessory for both the Model of 1917 and its successor the M1917A1.

RIA Museum Jodie Creen Wesemann

Drawing D1804A an alternate method of manufacture that relies on spot welding rather than rivets was developed in early 1942.  According to Iannamico in Hard Rain the Murray Corporation fabricated this alternate design.  Murray who pre-war made automobile sheet metal parts and gas tanks is best known for making children's wagons, bicycles and pedal cars and today riding lawnmowers.


RIA produced experimental flash hiders for the .30 caliber air cooled BMG’s during WWII including an attempt to adopt the M1923 flash hider to the M1919A4.  This whole series of “beer can” styles all suffered from the same defects.  They were relatively large and difficult to maintain as the vent ports plugged up with carbon deposits after extended firing.  Plugged vent ports would increase booster chamber pressure raising the rate of fire and the specter of damage to the air cooled weapons because their gas assist booster feature not present in the water cooled guns.

Jeff Prater Iron Creations LLC

 At least one, and likely several of this type were modified and attached to a M1919A4 barrel jacket by means of a modified front barrel bearing plug and sent to Aberdeen Proving Ground for testing in 1943.  The tests were not successful and in 1954 a left over jacket, bearing and flash hider showed up in a scrap barrel in a salvage yard behind the Proving Ground Museum where it was rescued by Jon Wilkinson a member of the 9701st Technical Service Unit stationed at Aberdeen.

Jeff Prater Iron Creations LLC

The story of this find related to the author by Mr. Wilkinson goes like this:  Jon saw the parts in the scrap barrel thought they looked unusual and wanted them.  The guy running the scrap yard told him that the barrels were pre weighed for sale as scrap, and if he wanted anything he would have to come up with an equal weight in steel for replacement.  Jon and his buddy Val Forgett , yes, the Navy Arms Val Forgett,  were leaving the post that day and noticed some railroad track construction underway so they stopped and filled the trunk of the car with tie plates to swap for parts that they wanted from the scrap barrels.  Jon displayed the A4 jacket/flash hider at an Ohio gun show in March of 2012 where Jeff Prater of Iron Creations LLC spotted it and decided it needed a new home.  Jeff took some pictures and sent them off to the author.  You just can’t make up stuff like this.

Eventually RIA’s flash hider R&D focused on the fairly obvious, the cone feature of the MG 08/15.  The cone shape tended to minimize and direct the flash to the front of the gun, reduce the low light ball of flame display and somewhat diminished visibility of the flash from the flanks.  The troublesome and complicated baffles and vent holes were eliminated.

RIA Museum Jodie Creen Wesemann

The M6 design for the M1919A4 Fixed and Flexible models which would also fit the M1919A5 included an integral front barrel bearing and a booster chamber eliminating the one or two piece front barrel bearing and muzzle plug and screwed directly into the barrel jacket staked in place with the usual band (lock ring). 


Silvan Arber photo

 Late style M7 flash hider with chrome lined booster chamber on an RIA purpose built M1919A6 circa 1955.

 The M7 flash hider for the M1919A6 replaced the cap style booster and the M8 design for the M1917A1 water cooled gun used a modified muzzle gland with the double male threads rather than the original gland.   The drawings for M6 and M7 have an original date of July 7, 1945.  It is not likely that any of these ever made it into combat in WWII.  All of the cone style flash hiders could be machined from steel or cast from perlitic malleable iron alloy commonly called ArmaSteel, Saginaw Steering Gear’s Malleable Iron Division trade name.

A good portion of RIA’s immediate post WWII activity involved the overhaul and refurbishing of all manner of equipment, especially small arms, and preparing them for long term storage.  This required the production of replacement and maintenance spare parts which they were doing in house.  M6 and M7 flash hiders were being produced  in small quantities as early as 1947.  While the M6 design remained virtually unchanged throughout production the original M7 design with a booster chamber diameter of 1.265 inches was apparently causing reliability issues in the M1919A6 so the chamber diameter was increased to 1.400 inches in August of 1948.

 The first mention of any mass production of M6 and M7 flash hiders comes from RIA’s Manufacturing  History for Fiscal Year 1950 (1 July 1949 to 30 June 1950) which also mentions R&D on an aluminum .30 caliber flash hider but does not indicate what .30 caliber weapon it was for.  Fiscal Year 1950 flash hider production was 17,990 M6 and 8,961 M7 flash hiders followed by 10,900 M7’s in FY 1951, 14,014 in FY 1952, 19,194 in FY1953 and 3,277 unidentified types in FY1954.

                                     RIA Museum Jodie Creen Wesemann

In August 1949 The War Department issued a Modification Work Order to replace all M1919A6 cap style boosters and M7 flash hiders with the 1.265 inch booster chamber, front barrel bearings and bipod retaining rings that were in the field with the new M7 having a 1.40 booster chamber and a redesigned front barrel bearing and thicker retaining ring.  The MWO did not cover weapons in storage and for reasons not known the MWO was rescinded by Department of the Army Circular 310-66.

                                                 Author's photo

The M6 flash hider is supposed to be marked 7162300 following the drawing/parts number naming convention adopted in late 1943 for new parts for either an existing or new weapon.  Some M6’s are mismarked C7162300 due to widespread confusion about including the drawing letter size in the imprint on the part.  Birtman Electric Company produced M6’s usually have the number near the open end of the cone, RIA production on the booster section.  M7’s are marked with the 7162303 drawing/part number there maybe mismarked C7162303 flash hiders lurking out there.  Maker’s markings were not required.  M6’s have the standard .718 booster orifice and M7’s the .812 opening, both designed for U.S. Caliber .30 ammunition standard ballistics.   The M6 has 1 inch wrench flats at the base of the cone to aid in removal.

When the Korean War started RIA farmed out some M6 production to Birtman Electric Company a Chicago firm that manufactured home appliances and had a production facility in Rock Island, IL.  Packaged M6 flash hiders with Birtman labels are quite common, usually found with packing dates from 1951 to 1953.  M6 packaging included a new band (lock ring) as the bands were not intended for reuse after initial staking.  Birtman also produced 3.5 inch M20 rocket launchers (bazookas) along with toasters and vacuum cleaners, there’s nothing like a little diversification.  The company was purchased by Whirlpool, the appliance maker, in 1957.  Every time the author loads the dishwasher the heritage of the bazooka and the M6 flash hider makes pushing the start button much more interesting.

While the M6 and M7’s were manufactured in quantity before, during and after the Korean War most of the official wartime photos seen by the author do not show either of these parts.  Documentation after July 1957 gets rather sparse as the air cooled BMG’s were being elbowed out of the way by the M60GP machine gun and the primary source of Browning information, RIA, and by association the RIA Museum, lost engineering support and manufacturing oversight for machine guns when this responsibility shifted to back to the Springfield Armory.

  Tom Chial photo

This photo shows the interior of a chrome plated M7 flash hider marked with part number 7162303-SA.  The author surmises that the M7's with the smaller diameter booster chamber were reworked and chrome plated, this one at Springfield Armory.

The last official documentation known to the author of the air cooled BMG’s are the 1970 Depot Maintenance Work Requirements produced by the Army Weapons Command at RIA and the 1969 TM9-1005-212-25 for the M1919A4, M1919A6 and arguably the best of the breed the M37.  These publications show only the M6 and M7 flash hiders as component parts, the M37 continued to use a booster bearing arrangement lacking any flash hider.   This document also refers to the interior of the booster chamber for the flash hiders being chrome plated.   Why the Army continued to produce a document, the DMWR, related to inspection and overhaul of a weapon displaced 17 years previously in combat ready units is not known.

                                                Carl the Jackal photo

Modified M6 flash hider for Canadian C1/C5A this flash hider is marked C7162300 and is sleeved down to .695 to insure reliable operation with 7.62X51 NATO standard ammo in M13 links.


Rock Island Arsenal Museum staff, Jodie Creen Wesemann and William E. Johnson

Lucky13, amish bob, Tim Gaine, Chris Guska, Jeff Prater, BMG Parts Inc., Jackal, Jon Wilkinson, Tom Chial, BMG Parts Inc. Silvan Arber and everyone who has helped with pictures, comments, and personal recollections. 

Together we have covered lots of ground, but there's still more to do and every day I learn (or relearn) something.   I hope that everyone enjoys reading this material as much as I enjoy the research.





















                              CREDITS AND ACKNOWLEDGEMENTS


Thanks to the RIA Museum staff, especially Jodie Creen Wesemann for their help in copying drawings and photos.


My good friend who shares the Browning obsession, Rollin Lofdahl has been a great help with pictures and real world knowledge and general advice on this and many of my other projects.

Thanks to BMG Parts INC. for use of the A6 booster photo.


A special thanks to amish-bob an important source of information and pictures of some really rare stuff.

Carl the Jackal and fjruple contributed to the Canadian C1/C5A1 booster information.


Thanks to all the members for the m1919a4.com forum for their help in piecing together the Browning story in excruciating detail.