1921/28 Navy Jamming

[usmcarizona]

Hello everyone,

I began collecting NFA firearms about 5 years ago.  I would have began collecting sooner, but I didn’t have the resources!   My first purchase was a Colt Thompson 1921 and my third purchase was a Colt Thompson 1921/28.   I was hooked the minute I picked one up!    I rarely shoot the 1921 as it is pristine, the 21/28 is a rebarreled “shooter” that I shoot often.  I mainly shoot it with drums because I often experience jams when using 30 rd stick magazines.

I was out shooting yesterday (Memorial Day) and decided to investigate the source of the jamming as there were two other Thompsons on the range and I could change out parts and magazines.  Based on our troubleshooting, most jams occurred when the magazine was feeding from the left side.  We used the same magazine on the 28A1 and it worked fine.   Upon further evaluation, it would seem that our feed ramps have different geometry.  My 21/28 seem to have more material with a slight ledge and the 28A1 seemed to have a more steady ramp with no ledge.   

Troubleshooting process:

1. Switched lowers-  Both lowers experienced the same jamming problem

2. Switch bolts- Both bolts experienced the same jamming problem.

3. used Magazines that functioned in the other Thompsons.   Would still jam in the 21/28.  

4. Pushing up on the magazine fixed the issue, but would cause the failure to extract issues on occasion.   

 

The first two photos are from the 1928A1 (smooth), the other three are from my 28 Navy.  Notice the impact from the case jam.  

 

 

My questions-

1. Has anyone else experienced the same type of jamming in a Colt 1928 Overstamp?  

2. Does anyone recommend any fixes?   

3. I’m located in Phoenix, AZ- are there any good TSMG smiths in the area?

 

Thank you,

Clay

[jim c 351]

Clay,

I didn't learn much from your pics, but I did have a similar problem with a Bridgeport M1928A1.

My gun fed perfectly from the drum and would fail to feed from the left side of stick mags.

I traced it back to the cartridge seat on the front end of the bolt.

I did some polishing with a dremel tool and solved the problem.

Best of luck,

Jim C

[gijive]

Are you sure you are not shooting semi-auto magazines in your 1921/1928?  The would be modified by the hole in the back being drilled out to an oval shape.  The reason I mention this is that you said you had to push up on the magazine to get it to feed properly.

 

It also could be the re-barreling of the gun.  If the gun was re-barreled with a West Hurley barrel, they have been known to have tight chambers, not to the original specifications.

 

It is also possible that the feed lips of the magazines are out of spec.  I would check the magazines first.

[colt21a]

mag first as jive says and the rebarrel. seems that looks messed up at first glance when something looks not right when you look at it.{Yeah i have seen a few of all Thompson models} check it all out.these stens did shoot a few rounds from  a mag before they fouled up. guess even fifty years in ground, did not hurt too bad.

[usmcarizona]

2 hours ago, jim c 351 said:

Clay,

I didn't learn much from your pics, but I did have a similar problem with a Bridgeport M1928A1.

My gun fed perfectly from the drum and would fail to feed from the left side of stick mags.

I traced it back to the cartridge seat on the front end of the bolt.

I did some polishing with a dremel tool and solved the problem.

Best of luck,

Jim C

Jim,

Thank you for the feedback.  Yes, those are horrible photos!   I regret not documenting the issue better.   Regarding the Cartridge seat, what did you Dremel exactly?   Thanks!  

[usmcarizona]

1 hour ago, gijive said:

Are you sure you are not shooting semi-auto magazines in your 1921/1928?  The would be modified by the hole in the back being drilled out to an oval shape.  The reason I mention this is that you said you had to push up on the magazine to get it to feed properly.

 

It also could be the re-barreling of the gun.  If the gun was re-barreled with a West Hurley barrel, they have been known to have tight chambers, not to the original specifications.

 

It is also possible that the feed lips of the magazines are out of spec.  I would check the magazines first.

GIjive, thank you for the reply.  We used a wide variety of USGI issued mags and still experienced the same problem.     When I pushed up on the magazine I change the feed path which I’m sure effected the feeding geometry.   The jamming happened at the feed ramp, with a live round, after extraction, but I will check the chamber tolerances.   

 

Thank you!

Clay 

[timkel]

Do you have a few dummy 45acp cartridges? Cycling the dummies through the action may help narrowing it down.

[jim c 351]

Clay,

I hooked the rim of a cartridge under the extractor and tried to straiten the cartridge with my thumb. It was difficult to straiten.

I used layout blue to determine where , on the bolt seat, it was preventing the the cartridge from smoothly locking in place and polished that area.

Don't over do the polishing. Use very fine grit wheel's.

Best of luck,

Jim  C

[TSMGguy]

Agree, make sure the 30 rd. mags (and the mag catch) have not been modified. I'd also drop a NOS USGI mainspring into the gun as some of these symptoms sound like the result of a weak spring.

I bought a magnificent matching NAC M1928A1 years ago that came with many USGI XX and XXX mags from the previous owner. He'd divided them into stacks of mags that worked and those that didn't. Every one was NOS or close to it. All worked great after replacing the gun's recoil spring. I found new homes for the mags that had been modified with elongated mag catch holes.  

Edited May 31, 2023 by TSMGguy

[Frankford]

Sounds like a weak mag catch spring. 

There is alot of problems with original springs, always under pressure in old guns.

Also check the mag catch for complete penetration, lift & lock up with the mag. They do wear.

 and yes, you could have the same problem in both lowers.

[TD.]

usmcarizonia,

Has any of the suggestions helped with the problem? After reading the thread, I wonder if simply changing bolt's would be worth a try.

[Rudy]

I'm with gi jive.  I think a few semi mags have migrated in to the mix. 

[deerslayer]

Lets see a head on shot of the feed lips.  Most are squished down and out of shape to one degree or another.