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Thompson M1


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I recently got my new M1 TSMG out of ATF Time Out. First time at the range. It sometimes doubles in semi auto fire. Also it "runs away" for a few rounds in full auto after the trigger is released.

 

From my limited knowledge, I suspect sear/bolt interface issue. Both the sear trailing edge and bolt notch look ok, i.e., not dinged up. Could it be a weak sear spring? Any thoughts are welcome. It's new to me!

 

Thanks,

 

Bill

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This is a topic that appears here on a regular basis. When the gun runs

away it is because the bolt recoils far enough to eject the case and feed the

next round but not far enough to be held by the seat. If anything a weak

recoil spring would prevent this as the bolt would more easily recoil.

When you shoot the gun you must sharply and decisively pull the

trigger. If you are slowly squeezing the trigger the sear will drag on the bolt,

slow it down and cause the doubles. This can also happen if you are trying to

shoot very short bursts.

Of course under-powered ammo would be the first thing to check. To check

the ammo

fire one shot on semi and the bolt should stay back at full cock.

It does take much rounding of the sear or notch in the bolt to make this

happen but you have checked this.

If nothing else works it could be that the barrel is shot out. The bore is

worn and not tightly sealed by the bullet, gas gets by the bullet reducing

power.

 

Bob

Edited by reconbob
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Thanks. It's a WWII Savage. Using Winchester white box and Federal. Just bought some Sellier & Bellot. Will lube bolt and shoot. Not ready to disassemble lower yet.;-)
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Don't dissasemble the lower. You can spray the internals with something like WD-40, and then put on a good quality oil, Mobile 1 synthetic, G96 etc. these were not designed to "casually" take the lowers apart. That would not have authorized by the individual soldier, but performed by a trained armorer.

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White box is usually a little light - S&B is a bit hotter. And inside the bolt cavity - lube it. I just use Rem oil.

 

I have lost steel plate matches (my excuse anyway!) with a gun that jammed after being fired only about 500 rounds - too dirty.

 

Bob is also correct on dragging your finger - don't. Hard to get used to if you were a trained target shooter - but you just gotta pull quick and get off quick. 180 degrees from target shooting.

Edited by giantpanda4
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Thanks for all the info. I was definitely trained to "squeeze" the trigger. Will have to undo that training! Steve, I will follow your advice on cleaning/oiling the lower.
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Clean the lower. Lube it well.

Just curious...what do you guys recommend using to lube the bolt assembly?? Tia

 

I use Rem-Oil or Clenzoil .

I use these on every part of the gun, in and out.

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Clean the lower. Lube it well.

Just curious...what do you guys recommend using to lube the bolt assembly?? Tia

I use Rem-Oil or Clenzoil .

I use these on every part of the gun, in and out.

Thx i need to get some

second on Clenzoil my favorite I use it it on all my guns full auto and semi

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#1 under powered ammo.

#2 lack of lubrication of bolt

Check these two items and report back.

Jim C

PS, its not a West Hurley, is it.

Ok, lubed fully. Using S&B ammo. Firing one round, bolt locks in SECOND notch. Not getting full recoil? Thoughts?

While observing a friend firing, lots of flash at breech. Is this normal? Barrel has good riling

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#1 under powered ammo.

#2 lack of lubrication of bolt

Check these two items and report back.

Jim C

PS, its not a West Hurley, is it.

Ok, lubed fully. Using S&B ammo. Firing one round, bolt locks in SECOND notch. Not getting full recoil? Thoughts?

While observing a friend firing, lots of flash at breech. Is this normal? Barrel has good riling

"Rifling". Fat fingers

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Hi OP,

 

Sorry to drop in but I've used a pretty simple test to verify the sear can catch the bolt.

 

With the gun empty (no ammo in or around, you know the drill), no mag, gun cocked. Now, w/o touching the trigger, pull the cocking knob to the rear of the cocking slot and briskly release the cocking knob.

 

If the bolt stops on the sear, things look decent in the sear/bolt area. If it skips over the sear and goes to battery, I'd say there is some work to be done.

 

Just a suggestion.

 

For myself, I have to check mine from time to time as I've got lighter springs in the lower for running my 22RF kits. Trigger finger is getting worn :)

 

Good Luck,

 

Grasshopper

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coastie,

For me the second notch is the furthest notch to the rear, which means your gun functioned perfect.

You will get flash at breach, but I can't tell what you mean by a lot.

Why did you quit after one round.??

Jim C

Jim,

I was told to run the one round test to see which notch engaged the sear. I thought if the bolt fully recoiled it would catch the sear at the front notch at the face of the bolt not the second notch. I am confused. Shouldn't the front notch catch the sear?

 

I can't quantify "a lot". I didn't realize there would be flash at breech, but now thinking about straight blow back, I can see why there would be flash.

 

I ran other mags. The gun doubled and tripled in semi (I am still trying to not "squeeze" the trigger) and ran away in full auto.

 

Bill

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Hi OP,

 

Sorry to drop in but I've used a pretty simple test to verify the sear can catch the bolt.

 

With the gun empty (no ammo in or around, you know the drill), no mag, gun cocked. Now, w/o touching the trigger, pull the cocking knob to the rear of the cocking slot and briskly release the cocking knob.

 

If the bolt stops on the sear, things look decent in the sear/bolt area. If it skips over the sear and goes to battery, I'd say there is some work to be done.

 

Just a suggestion.

 

 

 

For myself, I have to check mine from time to time as I've got lighter springs in the lower for running my 22RF kits. Trigger finger is getting worn :)

 

Good Luck,

 

Grasshopper

Thanks, sear catches bolt, but it's the front notch. When fired, it's catching the second (rear) notch and not fully recoiling.

Bill

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coastie,

OK, so you have done the one round test multiple times and the bolt always failed to lock all the way to the rear, correct???

I guess it could be something as simple as a overly strong, non original, bolt spring. Like a Wolfe spring. Or a weak sear spring.

Perhaps the sear trip installed backwards or damaged.

Perhaps you live near a forum member who could inspect your gun.

While waiting for a volunteer, buy a GI bolt and sear spring.

Jim C

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