Barrel Venting Mod for Hudson M1A1?

Is the det pin removable on the Hudson M1A1? I'm staring into the breech of mine and can't quite tell. I'd love to mod it for some action out the barrel.

Alright, so I think I've worked up the nerve to hollow out the plugged barrel.

Think .25" will be enough, or should I try to match the diameter of the barrel (about .40")?



Then I have to make a new hollow det pin, I guess. Cool, another project

Hi,

It looks like your Thompson is missing the main chamber part.

See post #4
https://mp40modelguns.forumotion.net/t1500-hudson-s-own-troubleshooting-guide

8ace

Only because I removed it to get the det pin out it’s safe & sound.

I think you will face challenges in your quest to create a "straight-through" venting barrel on the Hudson.

First, the chamber and detonator design doesn't create a good platform to use a hollow detonator because the screw goes through the back of the detonator.  Hence, the hollow detonator will be blocked by the screw unless you use a vented screw, as well - but the screw is quite small so not much material can be drilled out.

Second, I would highly suspect that there is a hardened steel insert cast into the zinc barrel, which will make it nearly impossible to drill to create additional venting.  A drill will probably start easy enough due to the zinc but will stop cutting as soon as it hits the insert.  Should be easy enough to check with a magnet to see if there is an insert in there.


If you give it a shot, please keep us posted!

ljerr2 wrote:

First, the chamber and detonator design doesn't create a good platform to use a hollow detonator because the screw goes through the back of the detonator.

 

Yeah, that was one of the first things I noticed. The whole thing needs to go. There are a couple design solutions for that problem, though.

ljerr2 wrote:

Second, I would highly suspect that there is a hardened steel insert cast into the zinc barrel

Ooooof, man I hadn't even thought of that. Magnet test just now says there's definitely something ferrous in there. About two inches worth from the look of it. You really think it's hardened, and not just some steel?Why would they be so cruel!

Ah that'll explain it.

I'm with ljerr2, I'd say it's probably a hardened alloy insert as most anti-tamper devices in modelguns are. The magnet test could also be showing Nickel or Cobalt used in Tungsten Carbide.

8ace

Japan has very strict laws on guns and the manufacturer probably had to almost guarantee an end user couldn't "convert" the model to shoot a lethal projectile.

Despite the insert, with the right tools, patience, blood and sweat.......you could probably drill the blockage at the risk of irreparably damaging the model.

Then you still have to deal with the chamber/detonator design. I am curious how you would plan to create a hollow detonator system.

Well I'm picking up this project again. I reached out for some quotes to EDM facilities near by to wire drill a hole through the steel plug in my receiver. If that's cheaper than an extra-length carbide drill, then that's the way I'll go. I'd rather EDM, since it'll be less stress on the receiver most likely.

In other news, I'm also upgrading the bolt to steel. Not much progress, but here's the blank I have ready for turning. The stock one was full of voids, and already bell-mouthed. This one'll be 4140 steel that I mayyyy heat treat as well. We'll see.

Yes the Hudson bolt castings are very poor quality. It'll be interesting to see your bolt when it's finished.

A couple of thoughts on your project.

1: Steel is massively over spec’d for a modelgun bolt. All of my projects have used unhardened 1113/1213 (230M07/EN1A) steel which is perfect for a lifetime of usage, also much easier to machine.

2: An off centre Carbide insert in the bolt face will stop any efforts to convert by add a firing pin later. When making custom bits it’s always good to ask “can this be converted”, if yes then change the design.

I hope this helps.

So THAT’s what that pin is all about on the standard bolt.
I kind of want to fit a real Thompson extractor, but I’d have to lengthen the bolt, which would mean moving the det pin back... might be too much scope creep for an already ambitious project.

Do you mean this pin

https://mp40modelguns.forumotion.net/t1326-thompson-bolt-identification

That’s the one! Mine isn’t a plunger installed with a grub screw, though. It appears to just be a press fit.

Blew right through a layout line, but from what I can tell it might still work. That front flat before the second notch seems to just prevent over-racking.

Still have to sort out the extractor. I’ll probably make another regardless. Worked a lot of problems out on this one.

Beautiful work! Keep us posted on your work.

Very nice indeed. Any idea what the weight of the new one is?

looking good and an essential upgrade.

@8ace it’s pretty darn heavy. I’ll weigh it when I take it back out of the lathe (drilling for the recoil spring). Hopefully it will still cycle. Rate of fire will be slower I’d imagine. Maybe 6061 Aluminum would have been a better choice?

Here's what I did to my bolt.

Looks like you hewed pretty close to the geometry of the Hudson bolt. I'll probably leave mine as is since I did a test fire today... and it cycled!



No extractor yet, but looking very promising. Still gonna make another one, since that little mistake earlier will bug me forever. Works just fine, though. The only difference is you can pull the charging handle back and lock it another half inch back from where you'd normally cock it.

Very encouraging to see it fire, though

Impressive!!!!!

Hope everyone is staying safe out there right now.

Still tinkering away on this bolt. Trying something out with an actual M1A1 extractor. Don't quite have it working yet, but looks prettayyyy good.

I'll be interested in the extractor fitting.

8ace wrote:

I'll be interested in the extractor fitting.

I mostly referenced some drawings for 1928a model I found. The extractor is almost exactly the same.



You have to account for the shorter length of the bolt on the Hudson, though, which makes the extractor a little stiffer.



That's what I'm trouble shooting right now. I'm trying to push the pivot point as far back as I can, but I may have to thin out the extractor as well to make the spring a little lighter.

Thanks for that. It looks easier than fitting the modelgun type (although I'm sure it's not)