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Advice On 1927-a1 Modifications?


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#1 Bob B

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Posted 04 August 2004 - 03:27 PM



Hope someone can help with this. I have an Auto Ordnance 1927-A1 Thompson carbine (Numrich, not Kahr). I've already made a few improvements, such as installing a new knurled actuator knob, polishing the bolt and feed ramp surfaces, relieving the magazine entry points and re-contouring the furniture in the style of the old '21s (looks terrific if I do say so myself). Can't wait for the ban to expire so I can afford a drum or two wink.gif .

I'd like to further modify the piece to more closely resemble a Model '21/'28. The modifications I'm considering include changing the safety lever to the paddle type, installing a new pivot plate and adding a rocker pivot lever (configured to act as a bolt holdback), installing a Model '21/'28-type stock with slide, etc. I checked the Numrich/Gun Parts Corp. website, but discovered the various parts I need are numbered differently for different models. For example, the pivot plate is apparently different for the '28 as opposed to the M1/M1A1 - likewise the safety and fire control levers. A call to Numrich/GPC did no good - they told me they couldn't tell me anything about parts interchangeability (on their own products no less) and suggested I consult a gunsmith.

The frame used on the 1927-A1 appears to be more similar to the M1/M1A1 frame than anything else. Am I safe in assuming an M1A1 pivot plate will have the same hole spacing/leg length? What about the knurled rocker pivot and safety levers - will the ones specified for the '28 model work?

My shop includes a couple of South Bend Lathes and a Bridgeport mill, so I can handle pretty much anything in the way of machining. All I need is some good advice on what will fit, and a lead or two on where others who have done these modifications found their parts! Of course, if anyone has a few spares lying around ...

Thanks in advance, and thanks for this great forum - I've really learned a lot just reading past posts!

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#2 ThompsonCrazy

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Posted 04 August 2004 - 04:29 PM

Bob,
The paddled safety will work just fine in a stock semi. The pivot plate is also interchangeable between the M1, 21/28 and semi but you will need to modify the lower frame if you would like use the selector. If not you will have an extra finger. I would try searching the archives for info as to how others have performed similiar modifications to acheive good looks and to allow the selector to hold the bolt open for drum install. I believe that there were some photos posted as well.
Hope that helps somewhat,
Brent
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#3 Grey Crow

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Posted 04 August 2004 - 04:51 PM

Bob,

I like many others here used the standard 28 paddles, and pivot plate. I do not believe that the procedure is listed on the board to actually do the conversion. PK has been setting up the frames for the feature.
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#4 deerslayer

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Posted 04 August 2004 - 10:14 PM

I'd say the detachable stock feature would be the next part. Get an adaptor plate from tommygunner.com that way you can use the standard 1921/28 type butt stock. This will require you to mill off the bottom of the reciever (seems like you have the equipment to do it) and attach the plate.

Set the compensator back, or better yet, if your state allows, go the short barrel rifle route.
Dan
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#5 Bob B

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Posted 04 August 2004 - 11:30 PM

Brent and Jack,

It's great to know the pivot plates and levers are interchangeable. Wonder why Numrich shows different part numbers for the different models - maybe the only distinction is that some are parkerized and others blued?

Dan,

I'd LOVE to go for a short barrel, but hate to go through the ATF rigamarole for just a repro carbine, and one of questionable quality at that. Heck, for the same trouble and fee I'd prefer to go the whole Class 3 route and really have something. Never been able to understand the reasoning behind the SBR restriction on Thompsons when, (a) they use pistol ammo and the barrels on garden variety 1911s are considerably shorter and in skilled hands just as deadly, (cool.gif there are so many modern guns out there that are shorter, lighter, and make better "gangster weapons" yet somehow are outside the NFA restrictions. Just seems rather arbitrary, but then logic seldom applies in matters legislative. Why is a Thompson any different than a "broom handle" Mauser pistol? Ah well ...

Wonder if it's legal to fit a solid dummy short barrel for display and exchange the long one when and if I ever take it shooting? (Had it since new in 1975 and haven't fired it yet!)

As for the slide mount adaptor, I removed the lug and milled grooves in the frame to fit the old 21/28 slides. I'll probably get one from tommygunner.com, but still need to find a lip-over buttplate to use one of the inexpensive boltless '28 stocks available from GPC.
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#6 Grey Crow

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Posted 05 August 2004 - 08:12 AM

Bob,

The difference in part numbers may be due to the style, you might call and see if the selectors are the pin type or paddle type.

The slide releases from TommyGunner.com are top notch.

I felt the same when it came to the SBR, but finally went the route, I'm glad I did. It's amazing what the 6" difference makes in appearance.


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#7 Sgt

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Posted 05 August 2004 - 09:21 AM

I agree with Grew Crow on that one. I've seen the SBRs and they do add one more level of realism. I certainly understand if you don't want to mess with the paperwork, though. As for the dummy barrel, unless you have the gun modified with a quick barrel release, most agree that a barrel change for the Thompson is a complicated job.
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#8 Zamm

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Posted 05 August 2004 - 10:53 AM

Bob,
Another alternative to the SBR route is to shorten the barrel 2" and weld the compensater
to the end, making the barrel a legal 16 inches and knocking off 2 inches on the way.
It makes a nice difference. If you do a search there are a few photos posted of this modification.
Best, Zamm
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#9 Motorcar

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Posted 05 August 2004 - 09:29 PM

Bob,

I got the pivot plate from Numrich/GPC. It was original blue finish never installed in a gun and WW2 vintage. I ordered it as a 1928 plate and it dropped right in. GPC messed up with the safety and rocker pivot paddles for the '28, they sent a pin style safety and a rocker..not the lever..so I gave up on them. Got the paddles from Sarco and the safety plopped right in also. It will be going to the Master PK for his hold open feature, slide milling and polishing-refinishing. Good luck with your project, I'm sure you will be happy with the end result.
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#10 Bob B

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Posted 06 August 2004 - 07:36 PM

Just wanted to say thanks for all the thoughtful (and useful) advice. Was able to find from several suppliers a few of the things I'll need, but still having difficulty tracking down the paddle-type safety and rocker levers. Tried Sarco but they're out of stock (they have the pin type).

I still have a bit of a puzzle regarding the correct drilling location for the rocker lever. The machinist's shop drawings I have indicate a through-hole diameter of 0.185" enlarged to 0.300" on the left wall of the frame, and 2.570" rearward from the magazine slide surface. Unfortunately, as detailed as these drawings appear to be, the vertical dimension is missing. Does anyone know the spec dimension from the bottom edge of the trigger frame housing to the selector lever centerline?

Thanks again.
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#11 Zamm

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Posted 08 August 2004 - 08:03 AM

Bob,
Thought I would post this also, get my FTP program running again.
These are drawing for a 1928 frame.

user posted image
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#12 Zamm

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Posted 08 August 2004 - 08:09 AM

You know,
I have no idea about who produced these drawings or how acurate they are.
Got them on eBay as a collectable... But, have a look at the lower right .
Final proof for any skeptics that INDEED, manufacturers where instructed
to fill there letters with white - from the factory. smile.gif
Man, is this not like finding the second gunman in Dealy plaza or what!!! laugh.gif
Zamm
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#13 Grey Crow

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Posted 08 August 2004 - 09:19 AM

The disconnector will also need modified to allow the rocker to go through the frame without interference.
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