M3 Grease Gun semi-auto conversion?

[Kano383]

Does anyone have pictures or drawings of a semi-auto conversion for the trigger mechanism of a M3?

I need a conversion for the original open-bolt system, not one that replaces the bolt and entire trigger mechanism like in the Valkyrie gun.

Thanks!

 

[boom boom]

Not something done here due to Batf regulations in the US.

 

[Jim K]

You might be able to design a trigger system with a disconnect, but none ever existed originally. The M3/M3A1 SMG fires so slowly (c. 450 RPM) that no semi-auto version was ever made; single shots are easily obtainable by trigger control.

Jim

 

[barnbwt]

Check out some of the popular gunbuilding sites; I'm certain someone has built a semi-auto striker-fired version by essentially chopping of the tail of the bolt & using it for the seperate striker. If open-bolt semi-auto is legal where you are, the same trigger group conversion would function to hold the entire bolt out of battery after each shot. Another approach on this front would be to examine or borrow parts from the M31 Suomi or CZ26, which both have compact & effective "trigger over-travel" based disconnector systems (likely sufficient if your authorities are okay with open bolt operation; in America positive mechanical sear disconnectors driven by the bolt striking the disconnector are generally required, since they cannot be converted to automatic *quite* so easily, but open-bolts are easily convertible regardless how the trigger is arranged so the weaker/simpler over-travel scheme may still be acceptable)

But whether that is legal depends on your local laws, as well as any additional 'denial' features that make re-converting to full automatic more difficult. Here in the States, we not only have to completely rework the internals of the gun into a closed bolt semi-auto system, but also re-create the receiver from a destroyed original (we cannot simply modify the intact original, it must have been chopped into pieces with a torch first, then re-constructed while incorporating semi-auto features that make full-automatic impossible)

Though I hate the GG and think it was a totally junky and sub-standard SMG, I'm jealous of your access to a kit/gun; they go for big money here in the States, even chopped into pieces & with destroyed barrels they regularly go for nearly $1000. Very few of them in America; ironic given that we were the source for the stupid things and passed them all around the rest of the world.

TCB

 

[Kano383]

TCB, thanks. Laws here do not enter into these intricacies, which is a good point (the more complicated a law is, the more difficult it is to apply, and the more it tends to make criminals out of unsuspecting law-abiding citizens...). The licensing authority can take decisions based on sound arguments.

Makes a lot of sense to chop something down and weld it back together so that The Law is satisfied...

Anyway... I've held a few M3s, and the trigger system is so bloody simple that it's difficult - and not obvious - to modify it for semi-auto fire. Since the local law, although trimmer, still makes a difference between semi- and full auto, I need to find a way to convert one of these into a semi-auto. Open bolt is not a problem.

Looking for ideas...I was thinking to check the Beretta M12, it's also an open-bolt system, but with a semi- selector. Any idea where I can get good drawings of that one?

 

[barnbwt]

Laws here do not enter into these intricacies

Neither do they, here; they're actually quite vague. That's why we have the Bureau of Alcohol, Tobacco, and Firearms, which creates regulations that *do* define the specifics like I've described above. It's probably the same sort of situation in your nation as far as the local regulations part. Open-bolts were once legal here, but were ultimately found too easy to convert to full automatic; if that is not yet the case for you, you'd be able to use very simple open-bolt semi-auto design solutions (many to choose from).

Since I assume that in your nation, like ours, the penalties for illegal machineguns are severe and prosecution aggressive, it's really best for you to consult with a local expert to make sure you're approaching this the right way (and also find & review the pertinent statutes). What's sad, is that because THR is US-based, we probably can't really discuss the technical particulars of open-bolt trigger systems that would be highly illegal here. The "NFA" (national firearms act, the law governing this stuff here) firearms subforum here or elsewhere would be better informed, and more likely to be authorized by the moderators to help you out. I'd PM one of the NFA forum mods here to see if they would be okay with you asking the question in a publicly-visible area (due to liability and gun politics, many folks are uneasy discussing these items, even though the information itself is legal)

It's even worse for import/export regulations, since you have not one but at least two nations' regulations making things difficult, if not impossible.

BTW, I wouldn't emulate the PM12 if I were you; Beretta put like a dozen parts in that trigger system. The Suomi and CZ26 have like three parts by comparison

TCB

 

[BBBBill]

Open bolt is more difficult to shoot accurately than a closed bolt. My Uzi was fired side by side with a full auto open bolt for comparison. That large heavy bolt really moves the gun around when the sear releases. Perhaps you should rethink and go closed bolt. Something like one of the Sten or Sterling conversions.