1919A4 Semi Auto Build

I got so tied up in this project that I forgot to take pictures from the beginning. I started with a 1919A4 parts set from Weaponeer group buy forum.

Here is a picture from 1919A4.com of what a parts kit looks like when I got it.

To build this gun into a semi auto configuration you must first assemble it with a semi auto right side plate, (which is considered the receiver of the gun) machine the internal parts to fit with the semi side plate, and use a semi auto trigger and sear. The bolt must also be machined to accept the new sear.

I used an Ohio Rapid fire 80% right side plate.

And a KMP semi trigger and sear which I ordered from Rapid Fire also.

The internals that need to be modified are the barrel extension, the lock frame, the bolt, and the accelerator. Clearance must be milled on the sides of the barrel extension, lock frame and bolt so that they clear a raised section on the inside of the right side plate. This raised section prevents the installation of the original full auto parts.

The bolt must also be modified for a wider semi auto sear so the original full auto sear will no longer fit. The lock frame also requires additional modifications. The slot for the trigger must be welded up and recut for a thinner semi auto trigger so that the original full auto trigger will not fit. The accelerator stop must be welded in place to support it after the side wall is milled thinner. The accelerator slot must be milled wider to accommodate the wider head on the semi auto trigger.

I will not go into detail of assembly because 1919A4.com has everything a person needs to know about building this project.

I assembled the gun with screws first so I could check the function and alignment of everything before riveting.

Then I removed one screw at a time and replaced it with the correct rivet, then squished the rivet into place using a bucking bar to support the back of the rivet, and an anvil on my air hammer.

After I assembled the gun and riveted it together I put it on the mill and milled down the rivets that needed to be flush, even with the side plate.

For the rivets that I planed on milling flat I used a flat anvil on my air hammer to just squish them out flat. The rivets that hold the bottom plate to the right side plate require a rounded head instead of being milled flat. For this I could not find the correct anvil for the hammer so I made my own. I purchased a ¾ air hammer chisel and cut the chisel end off with a cutoff tool. I then chucked it up in the lath and faced it off. Then using a ball nosed end mill machined a dimple in the end. I finished by putting a chamfer around the OD to reduce the size of the head.

This tool worked really well and made a nice round head on the rivet easily. The only thing that need improving is to put more chamfer at a sharper angle to reduce the OD more. When making the circular motion with the tool to form the head, sometimes the large OD of the tool head would hit the plate around the rivet and leave a mark.

After riveting was complete I assembled the gun and it’s ready to do some test firing.

The gun is very heavy and will need to be fired off of a rest. I will have to build a replica tripod for it, but that’s another project. After test firing lots of ammo and I am certain that no other work is needed, I will parkerize the gun to its original finish. Besides building a tripod I also want to build a linker to link the ammo and a transit chest to store it in just like the originals.