1919 Semi-Auto Only Mechanism

The 1919 A4/A6 Project

(semi-auto only conversion)

This project was implemented in 1996 using original 1919 de-milled full auto .30 caliber 1919 Machine Guns and re-engineered to allow semi-auto only operation.

I started out by examining all of the inner parts and getting an idea of the full auto operating system that John Browning so cleverly used. I immediately noticed that the trigger bar and sear were designed in such a way that, with a little modification, the trigger itself could serve as a disconnector bar for the semi-auto only action. I cut the end of the trigger off and made a block to weld onto the bottom to hold a new spring assisted trigger assembly. In doing so, I completely changed the system from full auto to semi-auto. A new sear had to be fabricated in order to accept the new trigger and in such a way that if the trigger was still actuated as the bolt came back to battery, the gun would not fire unless the trigger was reset by releasing it, hence the semi-auto action. The sear had to be wider than the original and the bolt that housed the sear milled out to the new sear dims. This was key to assuring that the full auto sear could not be reinstalled for full auto operation.

The right side plate had to be made from scratch due to the fact that it was the only thing that was not included in the demilled kits. Being the serial numbered part and designated by BATF to be the “gun”, the original right side plates were destroyed in the demilling process. The material thickness of the new plates were 1/4” thick, milled to the 3/16” thickness of the original plates but leaving three thick rails. These rails would serve as another key modification to assure that the original bolt and other original parts could not be inserted into the guns receiver.

The trigger housing, bolt carrier and bolt were all modified with deep grooves to match the bosses in the new side plate, completing the process of modification and complying with BATF's rules and regulations in the manufacturing and modifications of a full auto firearm to semi-auto only designation.

Since these guns were going to be offered for sale to the general public, it was important that a safety was implemented into the new design. For this I used a simplistic internal cylindrical cross bolt trigger block design that has been used many times by many manufacturing companies. When pushed to one side or the other, it would click into place by the use of two steel balls under spring pressure. In one direction the block would serve as a physical interference to the trigger, disallowing it to activate the sear. When pushed to the opposite direction, a relief cut in the barrel of the safety would then allow the trigger to fire the gun when pulled. A painted red groove was incorporated into the barrel of the safety and was visible in this position to show the shooter that the gun was ready to fire.

Ed Owens of the BATF firearms design approval dept. told me that this was the closest thing he had ever seen to using 99% of original parts in such a radical modification.