making a steel bolt

I picked up some demilled FBP bolt. They are the same as mp40 bolts except the firing pin is fixed to the bolt face. They are .5mm smaller diameter than the MGC bolt.

An original FBP bolt will fit in the MGC, but only up to the ejector. Since the bottom of the demilled bolt is milled off it clears the ejector.

The bolt handles do move. Mine were both damaged and loose. I'll try to repair them later.

After looking at the bolt it started to look like it could be possible to convert it into a MGC bolt. Started by punching out the bolt handle from the inside. Removed the extractor. Then cut off the firing pin.

Made the wings of the bolt bottom out of a piece of 1-3/8" round bar. Beveled the edges of the pieces and the bolt. Then tacked them on.

The center was made out of a piece of 3/16" square bar. Beveled the bottom right side to clear the mag and tacked it on. Then cut the cartridge pocket with a carbide burr in a dremel.

Reinstalled the extractor. Used a bolt for a temporary handle. Testing by hand it was able to reliably feed and extract the cartridges.

Now problems started. With an open spring the bolt didn't have enough force to strip the cartridge. It would stop about half way out the mag. That was with only one cartridge in the mag. If it was fully loaded the bolt would probably stop as soon as it hit the cartridge.

Tried a closed spring assembly next. The inside rear of the FBP bolt is larger than the MGC bolt. Since the spring assembly is held together by being pressed into the bolt that caused issues trying to keep the assembly together. The hole also isn't as deep so the bolt can't go back to the safety notch. The closed spring assembly was able to strip and chamber the cartridge.

Tried firing with both springs. The bolt wasn't able to recock even using the open spring. Ejection also wasn't good. Kept ending up with stovepipes. With the closed spring assembly there was just too much force and weight to recoil.

Tired both Marushin and MGC cartridges. The MGC seemed to work a little better. Not by much.

The bolt may be too heavy. There are several spots that weight can be removed from.

I have the same bolt, was wondering the same thing, curious how your making out.

The steel bolt is a ways away from being functional. The shape is right and feeds fine. It's just too heavy. I'll have to weigh the bolts and figure out how much needs to be removed.

A new recoil assembly is needed. For testing I can get buy with a 3d printed spacer and use the enclosed spring assembly.

The steel bolt is hard on the cartridge rims. Cartridges are no longer cheap or easy to find. Right now it seems pointless to have a steel bolt if it destroys cartridges.

I do have a few ideas for a semi disposable cartridge. That's going to take some time to test. If I can get it to work then I'll continue working on the steel bolt.

The factory bolt weighs 11.4oz. The steel one weighs 14oz. That's without a handle on the steel bolt so it will actually be a little heavier. Should be able to shave some off the steel bolt to get it down to close to the weight of the factory one.