Safety Devices and the Ground Type Air Cooled Browning .30 Caliber Machine Guns
By Charles Brown

From the adoption of the Model of 1917 water cooled machine gun through the M1919s and up to the adoption of the last of the breed, the M37, there were no parts on any of these weapons officially called a “safety.”

None of these weapons designs featured a trigger guard and to prevent accidental firing the Model of 1917, it featured a trigger lock that, when engaged, prevented lifting the trigger and firing the weapon. The trigger lock slid left to right in a cut milled into the back plate and was equipped with a detent to hold it in the locked position.

This device apparently was not held in very high regard by the troops, likely because it could be somewhat difficult to manipulate and under field conditions the latch slot could get filled with dirt or freeze during cold weather, making a bad situation worse. Since the latch required no tools to remove after the back plate was dismounted from the casing, troops field modified the weapons by discarding the latch. The practice of throwing the latch away became so prevalent that in August 1923 the Ordnance Department threw in the towel. The back plate drawing was revised and the cut for the lock was eliminated. Even though the trigger lock and back plate designed for it were dropped in 1923 the back plates equipped with the cut for the lock are not that uncommon, however, the locks themselves are somewhat scarce. When the air cooled Browning Tank Machine Gun Model of 1919 was developed from the water cooled Model of 1917 the trigger lock feature was retained.

With the adoption of the air cooled tank gun another problem cropped up. Loss of the water cooling feature on an automatic weapon that fired from a closed bolt raised the likelihood of a cook off. Normally, the mechanical energy of the striker or firing pin contacting the primer generates the heat energy required to ignite the propellant. Cook offs can occur in any weapon when the chamber temperature rises above the ignition temperature of the propellant that has everything necessary for combustion except for heat. The problem of residual heat buildup is much worse in a full auto weapon because of the rapidity of fire.

In Goldsmith’s The Browning Machine Gun, Volume I he notes that cook off tests of the tank gun indicated that firing a 400 round string got the chamber hot enough to produce a cartridge cook off about sixteen seconds after chambering a round. In addition to the obvious safety problem of the un-commanded firing, cook offs were especially bad news in the Browning design because the cartridge ignited with the firing pin retracted into the bolt. Primer set back in a cartridge operating in the 50,000 psi range could cause the primer cup material to flow into the firing pin hole in the bolt face. Given the way the case was held onto the bolt face by the T slot the fired case could be locked onto the bolt jamming the gun or breaking the ejector off the extractor.

To solve these problems without redesigning the weapon it was decided to equip the tank gun with a bolt latch, which was a flat piece of steel pivoting on a rivet on the right side plate with a notch in the top that engaged the bolt handle when it was pulled to the rear and the latch was raised. It could be quickly released by pushing it downward. The latch when engaged prevented a round from chambering and also promoted cooling. The bolt latch drawing 51-18-7 was dated November 20, 1919 some nine days after the armistice pulled the plug on the WWI meat grinder. The development of the M1919A2 retained the bolt latch in the design because it was essentially the tank gun with different sights.

On June 1, 1931, the original bolt latch drawing was re-drawn and renumbered B131295 to conform to the 1922 naming convention. When the M1919A2 drawings were adopted in late June of 1936, the bolt latch remained a requirement on it and all air cooled ground .30 caliber BMG’s until late May 1943. All of the prototype M1919A4 pictures and drawings seen by the author show bolt latches on both the Fixed and Flexible models.

There were three basic types of bolt latches, the original, which featured a finger flange on the bottom edge apparently to aid in either applying or releasing the latch, a simplified version lacking the finger flange introduced in October of 1920, and a shortened version shown on a drawing dated May 13, 1943, which was not likely produced as the bolt latch was eliminated three weeks later. Bolt latches were not required to be piece marked, however BA (Buffalo Arms) latches have been observed with either the drawing number/piece mark and the manufactures identification or both present.

The design of the M1919A5 adopted as Major Item 51-114 in May, 1942 continued the bolt latch feature with its signature cocking handle operated from the rear of the gun. The A5 had a built in bolt latch in the cocking handle similar to the Browning Aircraft Machine Guns Model of 1918M1 and Model of 1919. When the handle was pulled to the rear and downward pressure applied it caused a cut on the bottom of the retracting bar to engage the rear guide, a spring loaded plunger in the guide exerted downward pressure on the retracting bar holding the bolt to the rear. The M1919A4E1 fielded in 1952 as a temporary stand in for the M37 also had this feature. When the M37 finally appeared it had a positive engagement push button lock on the rear cocking handle guide that when applied prevented the retracted cocking handle from being jarred loose by road vibration or being bumped by personnel allowing the bolt to close.

In the fall of 1942 Aberdeen Proving Ground began testing cast 1919A4 parts manufactured by Saginaw Steering Gear including a cast casing. Mounting the bolt latch on the cast casing caused problems with tripod attachment and even though the cast casing passed muster it was not adopted and somehow the difficulties with the cast casing led to dropping the bolt latch on all M1919A4’s even though conventional weapons did not have the tripod issue.

The right side plate bolt latch rivet hole was eliminated by Revision 14 to the drawing D35411 and the Draftsman’s Work Order dated June 2, 1943 removing the hole carried the notation “MANDATORY MUST BE APPLIED IMMEDIATELY.”

In the opinion of the author bolt latches were dropped on new production A4’s very quickly. The author has viewed pictures of a Buffalo Arms M1919A4 serial number 478883 rebuilt into a M1919A4E1, which by serial number was one of the last out the door at Buffalo when they ceased M1919A4 production at the end of June 1943. It has no bolt latch rivet hole therefore could not have had a bolt latch. Implementing this change on weapons in production was a fairly straightforward operation, likely removing the rivets and latches from the assembly line and one bit from the multi-spindle drilling operation on the right side plate would do it. Right side plates already produced with the bolt latch rivet hole simply didn’t get the bolt latch at assembly into casings.

The earliest pictures of the M1919A6 from the September 1943 Standard Nomenclature List and TM9-206 also dated September 1943 do not show the A6 with a bolt latch. Drawing 51-125-1A which is the list of authorized components and assemblies for the M1919A6 dated July 23, 1943 does not list the bolt latch as an authorized part.

There are pictures of a pre-production M1919A6 with a bolt latch in Goldsmith’s Volume 1 and some A4 models converted to the A6 configuration may have had bolt latches, but they were not required on purpose built M1919A6s.

The Base Shop Data manual for the M1919A4 dated in mid 1943 shows the bolt latch and a tool developed to tighten the latch rivet.

Using production figures from The Browning Machine Gun, Volume 1, the author estimates that out of the approximately 437,000 M1919A4’s produced in the WWII period, about 284,000 were produced prior to July 1, 1943. This means about 65% were equipped with bolt latches.

Bolt latches were not officially removed from weapons unless they underwent a rebuild after the August 9, 1949 issue of TB ORD 366 the Overhaul and Rebuild Standards for Small Arms Material, which specifically stated that the bolt latches were to be removed. No Modification Work Order has yet been discovered that would have removed bolt latches on weapons in the field or in storage. It does not appear that the bolt latch or attaching rivet could be ordered as a maintenance part after January, 1944.

When the M37 was adopted it was equipped with a new design back plate featuring a quick release latch for dismounting the back plate and a positive trigger lock now officially called a safety.

One other safety device was mentioned in the first M1919A4 Basic Field Manual FM 23-45 issued in 1940. The instructions for clearing the gun included the following steps: after raising the top cover and removing the ammunition belt the bolt was to be pulled to the rear removing any live cartridge in the chamber and, “As an additional precaution, a wooden clearing block will be inserted between the face of the bolt and the rear end of the barrel.” This practice was likely a holdover from training for the Model of 1917 where the horizontal part of a wood T shaped clearing block held the top cover upright and the vertical part held the bolt face from the chamber. This method of rendering Brownings “safe” was clearly visible to the trainers on the firing line. The author uses a piece of yellow PVC gas tubing for the same purpose.

This article first appeared in Small Arms Review SAW (December 2012)
and was posted online on November 9, 2012


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