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Will an M1A1 bolt fit in a 1928A1 receiver?


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#1 imageaudio

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Posted 05 February 2019 - 12:43 AM

Hello All, 

 

I'm fairly new to the subgun collecting world.   I already own an MP40 and purchased a couple of FBP bolts to run a fixed firing pin system in the gun.  They work perfectly as long as I'm running hot ammo.  

 

Now, at long last, I'm shopping for a Thompson.   I'm leaning towards a 1928A1 model but wondering if I can run the M1A1 fix firing pin in a 1928A1 receiver?

 

I've purchased Iannamico's "American Thunder" book and as usual, was an excellent read and a great starting point for my Thompson education.    But still don't know if I can run the fixed firing pin in a 1928A1.   I'm waiting on the delivery of  "the Ulitimate Thompson Book" by Tracie Hill.    And of course, reading this form may be the best education as I find questions I haven't even thought about asking.

 

In any event, if someone owns a Thompson and has tried to do this and you care to share your experiences, it would be greatly appreciated.

 

Any other thoughts or advise for a Thompson newbie are always welcome.

 

Best regards, 

Scott C.


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#2 Grasshopper

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Posted 05 February 2019 - 01:13 AM

Hi,

 

I'll give this a shot.  Others will correct me.

 

Based on the 22RF conversion kits using a common bolt (aside from the cocking piece moving from side to top) I would think the M1A1 bolt would work in the '28.  There is the issue of how to cock the M1A1 bolt in the '28 w/o some machine work.

 

Another issue might be that the recoil spring location on the '28 is different than the M1/M1A1.  I don't have the numbers handy but that is something I noticed a few years back.  I have no idea why it changed.

 

Now is this a good idea in 45?  I'd think not as the '28 uses the blish lock and the M1/M1A1 does not have the blish lock.  Folks can discuss the merits of the blish lock again if they like.  Why is the m1 not that effected?  The rear of the receiver on the M1/M1A1 is thicker and IIRC has larger radii (sp) to increase strength.

 

Hope this helps,

 

Grasshopper


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#3 imageaudio

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Posted 05 February 2019 - 01:44 AM

Thanks for the info Grasshopper.

I’ve got several friends who could do the machining on the bolt but don’t know if it’s possible to modify. Tappng a new hole in the bolt would change the weight of the bolt and I wonder how this would effect the cycling operation, blowback, etc.


I guess a different question I should ask is how common is it to break a firing pin in the Thompson’s. Are there aftermarket bolts, firing pins, hammers, extractors, ejectors, etc readily available for the 1928 models?
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#4 ppgcowboy

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Posted 05 February 2019 - 02:06 AM

28 bolts are still readily available, as are most parts.
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#5 RoscoeTurner

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Posted 05 February 2019 - 04:19 AM

Why on earth would you even consider mixing the two?


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#6 PK.

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Posted 05 February 2019 - 10:04 AM

It's like shooting 454 in your 1906 SAA:  Dumb idea, you'll break it.


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#7 Colt Chopper

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Posted 05 February 2019 - 10:19 AM

Stick to the 28 bolt, firing pins are rarely an issue, and parts are cheap.
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#8 Petroleum 1

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Posted 05 February 2019 - 10:21 AM

Interesting idea but why make a Frankenstein out of the 28 it will run fine as is and parts are plentiful if you break something. If you really like the solid bolt buy the M1A1 too and have both! :-)

Edited by Petroleum 1, 05 February 2019 - 10:26 AM.

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#9 imageaudio

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Posted 05 February 2019 - 10:35 AM

The only reason I was considering running the M1A1 bolt in a 1928A1 was because the fixed firing pin system seems like it would never break and I was thinking I would keep the 1928 original but put the fixed firing pin bolt in when I take the gun out to the range.    I don't shot my subguns much, maybe 500-1000 rounds a year.   Just trying to protect the original parts if I get a semi-collectable gun but want to have some fun range time.    

 

This is the workflow I used for the MP40.   Keep the gun original but use an FPB bolt when at the range.     

 

From what I'm reading here on the forums, you guys don't think it's as much of an issue with the Thompsons?


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#10 bug

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Posted 05 February 2019 - 11:01 AM

In a word, no. The parts you are trying to protect are quite common. That is bolt, blish lock and actuator. In my opinion, the modifications you're considering would put the most critical part of the gun, the receiver, in jeopardy. I don't know enough about the MP40 to comment on that modification.


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#11 StrangeRanger

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Posted 05 February 2019 - 01:36 PM

From a standpoint of safety the M1928/M1 hammer and firing pin system is superior to the M1A1 fixed pin bolt.  There was an incident last year with an M1A1 where a fired case split and left some detritus in the chamber.  The next round could not fully seat but when the bolt went forward it fired the cartridge OUT OF BATTERY.  The resulting case rupture damaged the magazine but did not cause any injuries or damage the gun itself but it certainly could have.  An M1928 or an M1 could not have fired in that condition.

 

I realize this is an extremely unusual occurrence and that it involved some admittedly spotty ammo but it did occur.  Better safe than sorry.


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#12 Paul in PA

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Posted 05 February 2019 - 08:59 PM

And after reading "StrangeRanger's Post", there you have it. I actually pulled my Fixed Firing Pin bolt, and installed a M-1 Floating Pin for safety reasons. I read on this board many years ago of the issue of firing out of battery and how it was safer with the floating pin.

 

I second that 1928 parts are cheap and available, actually more available then M-1 parts these days. The fixed firing pin of the M-1A1 I feel will actually wear down over time.


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#13 Speeddemon02

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Posted 05 February 2019 - 10:47 PM

If safety is number 1 fixed firing pins are not the answer.  They cut down cost and number of parts and make the thing go bang when needed, but not worth it with any expensive transferable.


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#14 imageaudio

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Posted 06 February 2019 - 01:55 AM

Had not considered the firing out of battery issue. I totally see the potential for a serious problem there and that settles the case.

Imagine, the solution was to not over-complicate things. Who would have thought?

Thanks for the expert input and rapid replies.
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#15 GaryKeim

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Posted 07 February 2019 - 01:40 AM

Theres nothing wrong with the M1A1 or it wouldnt have been put into service. [Unwarranted, snarky comment removed]

The US military doesnt use crappy ammo, and neither should anyone else.


Edited by GaryKeim, 07 February 2019 - 10:25 AM.

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#16 Deavis

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Posted 07 February 2019 - 02:43 AM

You can buy many 28 bolts for the cost of one M1 A1.
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#17 Grease Gunner

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Posted 09 February 2019 - 10:53 AM

In using a M1a1 Bolt in a 28 receiver, besides making no sense at all; isnt the 28 receiver wider across

therefore the M1a1 bolt wont fit properly in the receiver???


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#18 Grasshopper

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Posted 09 February 2019 - 04:11 PM

Hi GGnr,

 

Bolts are the same height and width.  Note the 22RF kits use a common bolt with a different cocking piece.  Only the location of the recoil spring hole moved on the M1 vs '28.

 

Funny thing.  I've a friend with, not kidding here, a converted WH that started out as a S/A and was converted to a F/A.  It is transferable.  It uses a modified M1 bolt and the M1 recoil guide assembly.  Why anyone would convert a S/A before '86 is beyond me unless they just happen to have the S/A gun so only the cost of the stamp was involved.  IIRC, it does not have the cut-outs for the blish lock.  I'm not saying this is a good gun, good idea, or should ever be replicated but at least one exists.  If he sells it inexpensively, it may be a good candidate for 9mm or 22 RF conversion.

 

Enjoy,

 

Grasshopper


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