Re: M2 carbine won't run
Videos on the M2 from the 30's? I was under the impression that the M2 wasn't around that early.
One problem with some of those built up M2's is that the parts were not GI and often didn't work right. Not to say that is your problem, but a very common problem is a thin and/or soft disconnector lever that is bent wrong. It will work fine when worked by hand, but could trip the disconnector too early (or not at all) in FA fire. Also, some of the folks who did the conversion couldn't get M2 op slides and machined M1 slides. You can easily see the problems if that were not done correctly.
Do you know what is registered? If it is the serial number of the carbine, you can replace parts with no problem. But if a part (disconnector lever, disconnector or slide) is numbered and registered as the machinegun, you can't replace it.
Also, I don't know if there are any GI M2 parts left any more. When I built mine, I used parts I knew were GI, including an RIA disconnector lever. It ran perfectly.