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Shooting M1 30 rounds, firing rate seems to fluctuate


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Just the 2nd time I've shot my newly acquired M1 Thompson and I noticed that the firing rate seems to fluctuate going through a 30 round magazine. It feels and sounds like a flat spot. Is this normal? I haven't looked at the internals, what could go bad to cause something like this? It's an original GI, not a west hurley. I have a 22 second video I can email if actually hearing it would help, Thanks

Edited by Greystone45
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Well, if it is not ammo, then a simple check is if it does it on all mags. You might have a dent in one.

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Could be the follower dragging on sections of the inner walls of the mag body. You may wish to work the follower up and down with a dowel or stick to try to feel if there is any obstruction. I had to lightly grind and polish the edges of the overly tight follower of a 20 round mag to get it to keep from hesitating or stopping. Followers from a couple other mags worked just fine in the 20 round body.

 

Best of luck diagnosing and solving the issue. MP

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buy 100 rounds of fiocchi or other mid level ammo

 

use 3 different mags

 

see what the results are

 

10,000 rounds downrange from my guns in 3 years....only time ive ever had any fluctuation is when i mixed some different brands of ammo together...you can hear the gun speeding up and slowing down

 

id think a mag issue would cause jams...not speed issues...i think its ammo or something goofy with the spring/bolt catching

 

dry fire your gun while holding the charging handle--letting the bolt down slow....do this a few times...it should feel like glass...smooth...any kinks or knocks? ive only shot 1 other thompson than mine, but ive done this dryfire thing with a WH once and it was like light sandpaper running the bolt closed(thus my dislike for WH's)........your m1 should be smooth with no felt friction

Edited by huggytree
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Well, Merry Ploughboy reminded me what may be an issue for you too. Since you are a new shooter to the Thompson, you probably are exercising proper target shooting trigger control. That does not work... if you are squeezing off a burst, you are allowing the rocker to drag on the bottom of the bolt. Remove the bolt and see if there is the telltale line where the bolt was dragging...

 

With the Thompson, you have to be ON or OFF the trigger, no real in between. very hard to do after years of target shooting, I know.

 

This might explain why you are having an issue, but I am not sure form your description that it is the issue - just another thing to consider.

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If you can notice variation in the rate of fire, then the gun is probably shooting pretty slow. An M1 with an original "bright" bolt with separate hammer and firing pin should be shooting a pretty consistent 750 rounds per minute rate, as fast as an M1928A1, and faster than an M1A1.

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Could the firing pin spring be wore out and could this cause erratic cycling? I might have found the problem, I've found there is play in the hammer when moving it by hand, there is quite a bit of play in it and it's actually not sitting exactly right. Maybe the pin and hammer need replacing? thanks

Edited by Greystone45
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This is really difficult to correctly diagnose without a hands-one examination by someone knowledgeable.

I agree with TSMGguy. It wouldn't seem to be a firing pin spring issue in my opinion. if the spring was rusted and broken it would seem that failure to fire would be more likely. It wouldn't hurt to check and oil the spring and firing pin, I suppose, but consulting with a knowledgeable gunsmith that knows Thompsons and has the gun in-hand, would seem to be a better idea.

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The Thompson does have a heavy trigger.

If I am understanding what you are describing it could be related to no depressing the trigger enough.

The bolt could drag on the sear a bit.

Remove the lower and depress the trigger all the way to verify the sear (and other parts) are below the opening.

Ensure plenty of grease is used, and ensure the trigger is fully depressed and give it another try.

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