Calling Thompson M1A1 experts

[L34A1]

Hello all,
Took my newly made Thompson M1A1 out for a spin yesterday and it was not the best debut.

After my first magazine the rear sight falls off.....I am like WTF. Second...the magazines (all 5) kept falling out during the firing process.
The mags would lock in and could not pull them out manually but as soon as I started into a mag.....plop. So before I trash the MFG that did the work I will allow them to rectify at least the rear sight issue.

So a few questions..
1) Was the rear sight installed with rivets or screws? (M1A1)
2) Any one experience the mag issue or should I say the mag catch issue?

Happy Monday

 

[BWE Firearms]

1) Thompson sights were riveted on.
2) Is the mag catch for a semi auto or a full auto and which magazines are you using?

 

[arch stanton]

Read here machinegunboards.com

 

[L34A1]

Customer service is EVERYTHING in business. I heard from the MFG and it was not what I wanted to hear. Nonetheless I will be fixing my brand new Thompson build that I paid over $2K from Philadelphia Ordnance do do it for me.
The mag catch is a full auto and 4 magazines are Crosby and 1 is a Seymour.

 

[Battering ram NIB]

semi auto and full auto use mags holes in different places....i had a few egged out Thompson mags that would fall out of my SMG Thompson....found out they were modified by someone for a Semi auto...

i suspect this is your issue

 

[L34A1]

Nope....I have full auto mags and a full auto mag catch. I just got back from the range and all 5 of my mags work in another M1a1 Thompson with no issues. The mag catch stud on my M1a1 is .020 shorter than the other M1a1.
The 1 Seymour mag stays in and works in my gun but the 4 Crosby mags fall out under fire while the other M1a1 gun takes them all.....The bad apple I think is the mag catch

 

[SecondAmend]

IIRC, some Crosby mags were made out of spec. You may have to tweak the mag lips on them.

Best of luck.

 

[TheColtCollector]

Do you have a spare lower?

 

[Battering ram NIB]

are the holes on the mags perfectly round??
are you inserting them with the bolt back?

i bought tons of thompson mags and found a bunch with elongated holes...both from use and what appeared to be intentional.....i switched to some i had that appeared to be NOS and that problem disappeared...i do have trouble with mags if the bolt isnt back

mag latches are on GB and arent that expensive....get a new spring too.....taking the lower apart is fun the first time....not so bad after a few times though

 

[L34A1]

Bolt back yes then insert mag
Latch holes are round not elongated. The mags work in another M1a1 so its not a mag problem. I can not physically pull them out when they are inserted into my m1a1. They do lock in and the mag catch goes forward, but as soon a I start to shoot they fall out. If I hold the mag catch forward then they stay in and they function just fine. Mind you the Seymour mag works and stays in without issues.

 

[DINK]

Sounds like your mag catch spring is pooped out. Replace it.

There has also been some talk over on machinegunboards.com about defects in the hole that the mag catch spring goes into. If your gun is a new build, then there might be a problem in there. If the lower is an old GI one, it could have gunk, old cosmolene, blasting media or blueing/parkerizing salts in there. Take the catch off and see what you see in there.