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M1 and M1a1 Bolt Swap question


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Hello All:

New Issue ! I have a M1 Thompson with a M1 bolt in it. It is Stamped M1 and a smaller A1 stamped next to it so that

anyone can tell the A1 was added.Is this a M1 or a M1a1?

 

 

I also own a M1a1 thompson with a M1 bolt in it.

If I want to swap bolts, is there anything I should be concerned about?

 

Thanks

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The difference between an M1 and an M1a1 is an M1a1 has a fixed firing pin allowing a very slight possibility of an out of battery detonation. You will be better off with an M1 bolt. They are interchangeable.
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There was an OOB a couple of years ago at Tusco. A crappy Maxxtech factory round had a case separation and left a ring of brass in the chamber. The next round fed, jammed into the debris, and fired with the bolt not completely in battery. It blew the mag out of the gun but there was no damage to either shooter or gun. TSMGs are built like tanks, a less robust gun might not have fared as well.

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I was at an informal shoot decades ago. An out of battery discharge occurred on an M1 with an M1A1 bolt. The cause wasn't immediately determined but the result was clear. The receiver cracked through in the thin area between the ejection port and the mag well. (Yes, it was a West Hurley.)

 

Have countless soldiers used the M1A1 bolt without a problem? Yes. But you also use whatever the Army gives you (most of the time). You have the luxury of options and you're not compelled to use the "correct" bolt any more than you're required to eat MRE's. I've never (so far!) heard of or had a problem with an M1 bolt. Can't say the same for its successor.

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GreaseGunner,

If I remember correctly, a bunch of M1 stamped guns were rejected by the Ordnance Dept because of out of specs high rate of fire.

When the M1A1 bolt became available the guns were accepted and hand stamped with A1.

I have an M1A1 bolt in my M1 gun to get the slower ROF.

Use whatever you like.

Jim C

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GreaseGunner,

If I remember correctly, a bunch of M1 stamped guns were rejected by the Ordnance Dept because of out of specs high rate of fire.

When the M1A1 bolt became available the guns were accepted and hand stamped with A1.

I have an M1A1 bolt in my M1 gun to get the slower ROF.

Use whatever you like.

Jim C

 

Do you think the AOC M1 that were initially rejected by Ordnance Department due to the too high of ROF was possibly due to having had "sand cut" M1 bolts installed? The "sand cut" bolts seem to be much more uncommon then a standard M1 bolt.

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I have had a out of battery experience in a Thompson. Not with a .45 ACP but with a .22 in Merles conversion kit. The .22 bolt does have a hammer actuated during pin. Being a left handed shooter I do everything I can to reduce a out of battery from occurring and use a M1 bolt in my M1A1. My memory is I managed to avoid shedding any blood with the .22 LR case.

 

https://imgur.com/a/zk7yYbK

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