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Why M1 Bolt


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#1 kyle

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Posted 31 May 2004 - 02:00 PM

Can someone help me understand why a M1 bolt is inherently safer than a M1A1 bolt? Is it unsafe to use a M1A1 bolt? TIA!

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#2 The1930sRust

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Posted 31 May 2004 - 03:09 PM

I'll take a jab at this. With the 21/28/M1 bolt, it has to be in battery before the hammer/firing pin system is engaged by the wall of the receiver and the gun fires. With the M1A1 bolt, to save moneyand time, the complicated pin/hammer was eliminated and replaced with a simple metal tit milled to the front of the bolt. The firing pin as it were. True "slam fire" weapon. When the bolt moves forward, the round is automatically fired at battery--you hope. It is possible for the tit to hit the primer before the round is completely in battery, such as could happen if a case gets stuck in the chamber, or there is a jam, etc. Round goes off in the ejection port and you lose your face. At least this is why I think the M1 configuration is safer. With this, then, it is virtually impossible for the firing pin to strike the primer before it is time. Right, guys?
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#3 Norm

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Posted 31 May 2004 - 04:02 PM

The M1A1 is a "slam fire" set up, but so is the MAC 10, M11/9, UZI, SW76, etc.

I have never seen one "fire out of battry," but I am sure it can happen (especially on an out of spec gun or if there is a lot of crud in the chamber.)

I have seen several closed bolt guns "cook off" rounds. This, of course, is where heat detonates the round before the trigger is pulled (or at least before the firing pin hits.) This is easy to do with a Ruger Mini 14 and/or a Ruger AC556.

Just my $.02 worth!
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#4 SecondAmend

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Posted 31 May 2004 - 04:49 PM

The alleged unsafe mode of fire for an M1A1 Thompson is an urban legend dreamed up by Numrich and IMA so they could sell M1A1 Thompson buyers their huge stock of WWII surplus M1 bolts at $100 or so. ("wink")

Seriously, for $100 why risk blasting the person in the lane to the right of you? If you have an M1A1, put in the M1 bolt to be more safe and keep the M1A1 bolt for completeness. A M1A1 bolt is about $60 v. the $100 for the M1 bolt.
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#5 full auto 45

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Posted 31 May 2004 - 06:54 PM

Chris, you've been reading up on things haven't you? Sounds right to me, but I'm just a hapless old gun collector. Maybe I should give this up and start collecting stamps..............holy crap batman! Even those are expensive.

expensive stamps!


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#6 21 smoker

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Posted 31 May 2004 - 08:09 PM

I have first hand knowledge of the built in safety of the 21/28,M1 bolt...a case separated in the middle,leaving a half inch of 45 case mouth in the chamber....complete stoppage and undivided attention...this is a good thing..no damage and nobody hurt...I had STens,Sterlings,MP40s fire out of battery with the diminutive 9mm ammo and something always broke or someone got dinged a little...you can imagine the results with the robust 45cal....I, for one, am grateful for the engineering built into 21s,28s and M1s,my .02,out. wink.gif
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#7 1921A

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Posted 31 May 2004 - 10:08 PM

Chris has it right!

The M1 bolt is inherently safer than the M1A1 bolt. I have a piece of brass embedded in my cheek just below my right eye. This was the result of a "slam fire" in the ejection port that occurred when an extractor broke leaving a spent case in the chamber. It was not a fun experience. It has happened to others as well. If you can find a good M1 bolt it's well worth the money.

Keep in mind the moveable firing pin in the M1 bolt can do the same thing if it freezes in the exposed position. I saw this happen when a small piece of brass and a lot of gunk caused a stuck firing pin. Also, make sure the extractor is clean and functioning properly. Lack of proper "set" or a build of gunk under the extractor can cause it to fail setting up the conditions for "slam fire." Proper maintenance should minimize that possibility.

Surplus steel cased ammunition has also been linked to extractor failure in the Thompson that can lead to a "slam fire" condition.

Just my experience - hope the information is useful.

Greg Fox
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#8 Gunner

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Posted 31 May 2004 - 10:42 PM

Kyle, IMA has excellent quality M1 bolts for $100.
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#9 The1930sRust

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Posted 01 June 2004 - 05:24 AM

QUOTE (1921A @ May 31 2004, 10:08 PM)
Keep in mind the moveable firing pin in the M1 bolt can do the same thing if it freezes in the exposed position. I saw this happen when a small piece of brass and a lot of gunk caused a stuck firing pin.

Excellent point, Greg. I always clean and check the firing pin and spring by disassebling the bolt.
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#10 PK.

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Posted 01 June 2004 - 08:56 AM

I also have had personal experience (twice) where a case has separated, leaving a ring in the camber of my 28. The gun stops without fanfare or fireworks. Once the ring is removed all returns to normal.

I would not feel uncomfortable shooting good quality factory ammo in a “right” M1A1, but I would never shoot handloads in one. There are circumstances other than failed cases that can cause problems. The truth is that the M1 bolt is safer in any circumstance, and the separate firing pin is a revered deign of the Thompson.

In my lexicon, the problem described is more accurately called “discharge out of battery”. Any gun that fires from an open bolt is a “slam fire” gun.

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#11 must

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Posted 01 June 2004 - 01:27 PM

I had a premature ignition with a M1A1 bolt also. The round went off & flame went out the the ejection port (this was right next to my face too)!The round got stuck part way down the barrel. I bought one of those IMA-M1 bolts & it works great. It also looked like it was almost new too. The manufacture on the bolt was Savage.
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#12 Norm

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Posted 02 June 2004 - 04:10 AM

All joking aside; these stories are very good reasons to make sure you wear safety glasses at the range! cool.gif

If you don't, you might look like this guy after a misfire -----> wacko.gif

Norm

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#13 Bisley45

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Posted 02 June 2004 - 10:48 AM

definatley the M1 bolt is worth the money, been threw the cartrage case seperation thing, it's NO URBAN MYTH! check the old boards for my story...

BB
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#14 JTinIN

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Posted 05 September 2004 - 11:05 AM

Have had a few friends recommend running the M1A1 bolt in the M1 to eliminate any issues with firing pins breaking etc.

After reading this posting, think will stayk with the M1 bolt in the M1.

Edited by JTinIN, 05 September 2004 - 11:05 AM.

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#15 Sgt

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Posted 05 September 2004 - 12:49 PM

Guys--
Thanks for going into depth with this. That sort of thing is easy to miss, especially to the novice collector. I've always heard people changing out their M1a1 bolts, but never took this as seriously until I read this thread. Sounds like some nasty thing can happen and it is certainly worth the extra $100 to make it a safer gun.
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#16 Zamm

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Posted 05 September 2004 - 01:31 PM

Ralph,
Judging by your artistic expertise at rendering, I would
plead with you to switch out to the safer M1 bolt.
Talent would be a terrible thing to lose for lack of a couple of tools (lookers smile.gif
Cheerio, Zamm
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#17 Sgt

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Posted 05 September 2004 - 02:09 PM

Good point, Zamm-- I think I'm one of the fortunate ones whose M1a1 as converted back to the M1 design as part of the armory refurbish. However, it's still good information, because I might have tried some of my spare parts bolts out in it.
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#18 Tash329

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Posted 14 September 2004 - 06:38 PM

Im new to this board, and have purchased a Karr Thompson. I have read the posts and think I'll heed the advice given here and order a M1 bolt. My question is who is IMA, and are they the only ones carrying this both?

Thanks Rich
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#19 Bob B

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Posted 14 September 2004 - 07:45 PM

Tash329,

Before blowing $100 on an M1 bolt, I would check to be sure you actually need one. I could be wrong, but it's my understanding that the Kahr '27A1s, like their NAC predecessors, already use an M1 style bolt - that is, a sear-release firing pin rather than a fixed one. The Kahr guns may have other issues that require attention for reliability, but I don't think this is one of them. BTW, a fixed firing pin (i.e. an M1A1-style bolt) on a semi auto Thompson is strictly VERBOTEN, since that makes it a full auto weapon!

Since you're new to this game, welcome to the wonderful world of Thompson addic... uh ... enthusiasts! wink.gif

Bob

Edited by Bob B, 14 September 2004 - 08:29 PM.

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#20 Bill in VA

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Posted 14 September 2004 - 07:53 PM

IMA=International Military Antiques (www.ima-usa.com) Sarco used to have M1 bolts as did Gun Parts Corp. I also see M1 bolts (and a few other TSMG parts at the local gun shows, but in my experience they seem to be slowly drying up...keep your eyes peeled though.)
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