Thompson M1 sight keeps coming loose!!!

V

vtchopperdude

New member
Fellas, I'm at a lose. I have a Auto-Ordnance Thompson M1 that I SBRed years ago. The sight is held on with 4 screws that will not stay tight. Usually after 2 magazines they will loosen up and I actually lost one of the screws yesterday while at the range. I have used blue loctite, red loctite, and even had my buddy tac tig them on, and they STILL manage to rattle loose. Is there a rivet option that would work? I'm not a Thompson expert, but I would assume that the sight had to have been riveted on originally. No way the GIs were having this issue...

Thanks for yals advice
 
I’m surprised that it keeps coming loose even with all the fixes you’ve tried. Since your question has more to do with a repair issue and less to do with the fact this is an NFA item, I’d recommend asking a mod to move this thread to the gunsmithing subforum. You’ll probably get a lot more good answers there than you will here.
 
Just to be clear, are you talking about the Auto-Ordnance M1 semi auto??

and, if so, is the receiver steel??? The "lightweight" models (listed at about one pound lighter weight) used Aluminum alloy though I don't know remember if it was the upper, the lower, or both.

If your upper isn't steel, that could be why the screws don't stay tight.

I have one of the deluxe 1927A1s, all steel and wood. Never had any issues with anything coming loose.
 
ok, a friend of mine has one of those, had it switched to the SBR version a little while ago, after his approval came through. I'll take a look at it the next time I visit him.

If Loctite didn't hold, I would have suggested staking the screws, but if tack welding didn't hold, either, I'm at a bit of a loss...

usually, when screws come loose on one gun, but not on every gun of that model, its not the vibration alone that does it, its the vibration and a poor fit combined.

Its not impossible that the screws used are very slightly undersized for the holes they go in. In other words, enough thread engagement to hold but not enough to hold as well as they should. (you can tighten them up, but they work loose)

Have you contacted the factory about the problem?? Even if there's no warranty coverage, no one is better set up to work the problem than the people who made the gun in the first place. Talking to them about the problem costs nothing but a phone call /e-mail. Depending one what they say, it might be they won't need the entire gun, only the "upper" which IIRC is not the ser# part, and so is not a "firearm" for shipping purposes (and costs). Though I'd check on that bit carefully before mailing anything...

Give them a call, see what they say, at this point, what can it hurt??
 
"...if there's no warranty coverage..." vtchopperdude's warrantee was voided when he changed the barrel length.
Receivers are steel or AL. No mention of what model is what though. Think I'd re-tap for a slightly bigger diameter screw and stake 'em. However, because the Lock-Tite isn't working, I suspect it's a heat issue. Can't imagine how the receiver would get that hot though.
 
it's the steel receiver

I don't think heat is the issue; I think (I assume...) it has to be the percussion of the blowback that is just rattling them loose over time; I'm afraid to put too much torque on them, and break them off or strip them out; I have some rocksett left from my suppressor attachment installs; I might try that; my suppressor barrel attachments won't come off, even with heat...
 
Ok, I put some red Loctite on them again. We'll see how that holds up, but the staking idea may provide additional support. Has anybody staked a Thompson sight? With the design of the sight, I'm not sure how (what angle) to do the staking at. Also, with it being steel, would the staking even really work as advertised?
 
Loctite

Loctite is most effective if both the threaded hole and the fastener are squeaky clean. Use a good degreaser esp. in the threaded holes.

Heat is your friend when it's time to take it apart.
 
Well, I dropped some loctite on the threads, so we'll see during the next range trip if it holds up. I just am surprised that they come loose that easy after only 30 rds...
 
As others have mentioned, if the threads in the hole and on the fastener are not absolutely clean loctite will not work.
If you could run a tap in the hole, then degrease and brush the screw that would help.
I use Brake-clean for degreasing/cleaning. Cleans and leaves no residue.

After assembly let it sit for a few hours before shooting.
 
So I've done some searching on the interwebs and it looks like the sight screws coming loose is a common problem on these Thompson's made by Kahr arms. Several people on machinegunboards.com recommended having it "sent off and rivets installed." Has anyone done this, or familiar with who could do this? Since Kahr doesn't rivet them at the factory, I'm assuming that's not work they do.
 
Update:

I used AR15 gas key screws trimmed to fit, along with rocksett to hold them in, and additionally, staked the screws. Hopefully this time around they will stay put.
 
Fellas, long time update. I finally zeroed in on John Andrewski out of New Hampshire. Seems to be the go to guy for Thompson work. He got both my M1A1 and 1927A1 fixed up. He used rivets for the sights, which was originally how they came. He also did some other great work on the feed ramps to stop the occasional jamming. Among other things, he refinished my M1A1 in a nice war time parkerized finish, and finished my 1927A1 in Dulite. If anyone is having issues with their tommy guns, look up John!
 
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