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Very first Thompson build: some misc. questions (21 v. 28, parts resto


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#1 TehVice

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Posted 11 February 2020 - 10:30 PM

So, after lusting after a classic '20s-'30s era Thompson, but resisting for the better part of a decade, I recently decided that the '20s rolling around again just barely met the minimum level of justification to give in and splurge.

 

I bought a 1928 parts kit (adjustable Lyman rear sight, original finned barrel, knurled actuator, Cutts compensator, non-reinforcing bolt stock). Using what I've got, I'd like to try to build as close an approximation of a 1921 model Thompson, aesthetically, as I can (I'll have to overlook the lack of knurling on the selector levers, I know). I realize I've got some work ahead of me stripping finish, filing/stoning away tool marks, trying to blend out various gouges/scratches/burrs, smoothing out surface roughness, re-bluing, etc.  However, while I'm waiting on an appropriate receiver, I'm trying to get a more developed picture of the scope of work necessary to accomplish this, to decide whether it's worthwhile (cost & time) to pursue as a longer-term project; the alternative being just building it back up as an M1928 model.

 

I'm aware of the contrast in level of finish quality between a 1921 Colt and 1928 Savage gun, but to what extent was there a similar difference in the fit of/degree of play in the parts between the two models (fit of the stock latch frame/slide to the lower frame, for example)?

 

Next question: the barrel I have has the compensator pretty firmly affixed, sans cross-pin. There was very clearly a pin present once, but it's been removed at some point. My ability to see muzzle threads through the cross-pin hole, coupled with the fact that there are what appear to be vise-jaw indentation marks on the sides of the compensator make me suspect that in the process of removing the barrel from the original receiver, the compensator may have been super-torqued onto the barrel. It definitely doesn't want to loosen through any reasonable amount of hand force, so I'm not sure how to proceed in attempting to unthread it. Has anyone ever dealt with a similar problem, or know of a method/tool/setup to apply torque to unthread the two without without damaging either the compensator or the barrel?

 

Third question: 50 round drum magazines -- what's popular opinion on the most reliable reproduction examples? Are the Kahr-produced magazines still pretty questionable? I've noticed some Korean-made magazines on the market for a decent price and that seem to be getting decent reviews, but wasn't sure whether there's a consensus on what to choose for best performance for the money.

 

I realize this post is a sort of 'shotgun' of different questions, but if anyone has any information/advice on anything I've asked (or should have asked, but didn't), I'd really appreciate it!

 


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#2 ppgcowboy

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Posted 11 February 2020 - 10:51 PM

Are you building a display gun? Reliability should not matter as it Is non functional as far as the drum is concerned.
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#3 cbmott

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Posted 11 February 2020 - 11:37 PM

Talk to Richard at Tommygun Collectibles he has a guy who is adding the knurling pattern to WWII safety and pivot pins.


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#4 TehVice

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Posted 12 February 2020 - 12:56 AM

Are you building a display gun? Reliability should not matter as it Is non functional as far as the drum is concerned.

 

No, this will be a fully-functional gun, so I'm hoping to not have to tinker too much to get a drum feeding reliably.


Edited by TehVice, 12 February 2020 - 01:01 AM.

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#5 reconbob

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Posted 12 February 2020 - 08:28 AM

Are you in the USA? If so the manufacture of machine guns was banned
in 1986. You can't legally do it. Period. I know it is confusing because silencers
and short barreled rifles were not banned. To this day over 30 years later I often
hear people say they will "get a stamp" and make a gun, and they all knew a guy
who knew a guy that got a stamp. So you might want to change your plans
before you get too deeply invested.

Bob
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#6 Tiz

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Posted 12 February 2020 - 08:49 AM

I agree with Bob. You DO NOT want to run afoul of the ATF. It will defiantly ruin your day and many to come. Just buy a transferable and call it a day.


Edited by Tiz, 12 February 2020 - 10:54 AM.

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#7 reconbob

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Posted 12 February 2020 - 10:45 AM

Follow up comment on the compensator. Any number of things could have
caused the comp to lock up on the threads. Long experience has shown that
when the compensator and barrel are drilled and pinned, that sometimes the
thread will be damaged and sometimes not. I have removed hundreds of compensators
from barrels and found that after the pin in removed the comp will either unscrew
easily, or have to be wrenched off the whole way. The drilling of the hole for the pin can
deform the threads and as you unscrew the comp the bad threads are scraping along
and damaging the remaining threads as it is unscrewed.

If you have to use a wrench to get the compensator off you will not be able to screw
the comp back on until you dress the thread in the comp (with a tap) or on the barrel
(with a die) or both. There are special wrenches for removing compensators which
allow you to grip them without damaging them but I don't know where you could find
one since they are out of production. Obviously you don't use a pipe wrench.

Bob
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#8 ppgcowboy

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Posted 12 February 2020 - 10:55 AM

Where will you get the reciever.
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#9 Motorcar

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Posted 12 February 2020 - 11:15 AM

Are you in the USA? If so the manufacture of machine guns was banned
in 1986. You can't legally do it. Period.

 

You are assuming he isn't licensed to build a post May dealer sample like several of you out there are...Probably not but...could be.

 

I've noticed some Korean-made magazines on the market for a decent price and that seem to be getting decent reviews, but wasn't sure whether there's a consensus on what to choose for best performance for the money.

 

They are Taiwan produced, good quality and run fine. Do a search here and you will find pages of information.


Edited by Motorcar, 12 February 2020 - 11:17 AM.

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#10 TehVice

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Posted 12 February 2020 - 11:17 AM

Are you in the USA? If so the manufacture of machine guns was banned
in 1986. You can't legally do it. Period. I know it is confusing because silencers
and short barreled rifles were not banned. To this day over 30 years later I often
hear people say they will "get a stamp" and make a gun, and they all knew a guy
who knew a guy that got a stamp. So you might want to change your plans
before you get too deeply invested.

Bob


So, that's partially true. FFL holders can file and pay for what's called a "Special Occupational Tax" (SOT). There are a few different SOT types (dealer, importer, manufacturer, etc.). If you have an FFL and the 'manufacturer' SOT (also known as an '02 SOT'), you can legally manufacture and register new machine guns, with the caveat that they can only be transferred between other SOT holders or government entities. These guns are known as 'post-samples'.

I'd love to get a transferable 1921 or 1928 some day, but they're a bit rich for my blood at the moment, so the ~$3,500 post-sample build project won out.
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#11 ppgcowboy

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Posted 12 February 2020 - 12:08 PM

Great to know. This board can only answer questions with the information given them. Reconbob should be able to supply a 21 receiver that would fit your project perfectly.
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#12 Adg105200

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Posted 12 February 2020 - 12:41 PM

Sounds like a fun project! I've seen comps that have had vice marks and then I've seen and had some that were removed from the barrel without removing the pin without any damage to the comp or the internal threads.

Andrew
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#13 TD.

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Posted 12 February 2020 - 01:02 PM

TehVice,

Welcome to the Thompson forum. If me, and I was properly licensed and only thinking of building one post-sample Thompson, I would consult with reconbob at Philadelphia Ordnance (Bob Bowers) to see if it would be more cost effective to have Bob build you one. He has a lot of experience in this area. And that is probably where you are going to obtain an 80% or display receiver to begin your project.  

 

Good luck! 


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#14 Black River Militaria CII

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Posted 12 February 2020 - 01:26 PM

Small point here but a useful one concerning unscrewing any threaded joint where the threads could be damaged by a punch strike at thread joint (MP40  recoil spring housing cap), a hole drilled through both parts of the assembled threaded item, rusted threaded joint and other similar situations where thread damage can be aggravated when unscrewing the assembly. 

Unscrewing such joints without taking care will result in spalling of the metal of the threads. Spalling moves metal along the path of the threads and very quickly can freeze the joint as the spalling builds up creating greater and greater friction until no movement is possible. 

For unrusted assemblies, the first direction to turn the moveable part is to very slightly tighten it to break the bond. Then loosen it slightly and repeat tighten/loosen it a few times until it feels looser and even loose enough to turn further. Drip a bit of Kroil into the joint and let it sit to penetrate. Heating the joint will help Kroil move into the joint. When starting the unscrewing again, unscrew it very slowly a quarter turn and note if it feels like resistance is increasing. If it is, tighten and loosen to the same point several times to allow the threads to mesh more cleanly and reduce spalling. Unscrew very slowly past the previous point observing if resistance feels like it increases at any point. If so, repeat the previous step until the friction in the threads feels less. more heat and Kroil might be helpful. Once any potential for spalling in the joint is relieved the movement of the part that is rotating will feel smooth.

Another trick is to put a small amount of anti-sieze compound on the newly visible threads and screw the rotating part back to it's original position which introduces the compound into the threads and helps to smooth the contact of the threads in that section and also helps to loosen the remaining threaded part.

With joints that might be rusted, heating the joint and steeping it in Kroil for a few days so it can penetrate a ways into the joint can give an advantage to keeping the rusted threads from spalling. When first breaking the bond the rust itself will move in the thread contact areas and it acts as an abrasive. Same procedure as noted above follows with rusted joints with more heating and oiling of the joint if resistance is encountered. Hope this helps.


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#15 reconbob

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Posted 12 February 2020 - 07:43 PM

     If you want to be a Class 2 (manufacturer) SOT, you must first have an 07 (manufacturer) FFL.

Applying for an 07 undergoes greater scrutiny by the ATF.

 

     As a Class 2 you CANNOT transfer newly manufactured machineguns to other Class 2's unless

they have a Police Letter - a letter from a Police Department requesting that the gun be demonstrated.

The ATF has really tightened up on these letters - one or two words that say or imply the wrong thing

in the letter will cause it to be denied.  I have a new manufacture M1928A1 post sample receiver that

has been sitting here for over a year because the buyer cannot get the ATF to approve the transfer

with the letters he has provided, and originally he thought it would be "no problem".

 

    If a Class 2 goes out of business or changes his license then he can transfer his post samples

to other Class 2's without the Police Letter, but thats it. 

 

Bob


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#16 johnsonlmg41

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Posted 12 February 2020 - 09:19 PM

Spalling.....umm you mean galling.   If the barrel and compensator are spalling....with rust, you may as well throw them back in the lake they came out of?  LOL


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#17 Black River Militaria CII

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Posted 12 February 2020 - 10:22 PM

Jeez Jeff, that's the best you can come up with? I am just disappointed, I am, just so disappointed. Wassa motta, no bowling league tonight? You will notice with careful re-reading of my post that I said nothing about compensators or barrels, right?

OK, for example, the next time you have an MG08 or 08/15 booster that is beautiful on the outside but will not disassemble due to corrosive ammo damage to the threads please send it to me before you throw it into the lake.

I won't bother you with the list of the hundreds of thread assembled parts that have been saved in my little shop over the years due to careful efforts to disassemble them. Or the many letters and e-mails from the owners of those very parts expressing their gratitude for the concern for and the work of saving the parts. Didn't your Mom teach you in your "yout" that if you have nothing constructive to say just don't say anything? If not, there ya go. Better late than never. Compliments of Old Mother Bob.

BTW, have you anything interesting for sale?

Happy New Year!


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#18 TehVice

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Posted 12 February 2020 - 11:40 PM

Follow up comment on the compensator. Any number of things could have
caused the comp to lock up on the threads. Long experience has shown that
when the compensator and barrel are drilled and pinned, that sometimes the
thread will be damaged and sometimes not. I have removed hundreds of compensators
from barrels and found that after the pin in removed the comp will either unscrew
easily, or have to be wrenched off the whole way. The drilling of the hole for the pin can
deform the threads and as you unscrew the comp the bad threads are scraping along
and damaging the remaining threads as it is unscrewed.

If you have to use a wrench to get the compensator off you will not be able to screw
the comp back on until you dress the thread in the comp (with a tap) or on the barrel
(with a die) or both. There are special wrenches for removing compensators which
allow you to grip them without damaging them but I don't know where you could find
one since they are out of production. Obviously you don't use a pipe wrench.

Bob

 
Thanks for the info. I figured there must be some special tool out there, but hadn't come across anything in my (admittedly pretty cursory) research. I have a basic idea of a tool I could fabricate to get torque on the compensator without digging into it, but I'm thinking I might just try find someone properly experienced/equipped to tackle the job rather than risking it.
 
 

Are you in the USA? If so the manufacture of machine guns was banned
in 1986. You can't legally do it. Period.

 
You are assuming he isn't licensed to build a post May dealer sample like several of you out there are...Probably not but...could be.
 

>>I've noticed some Korean-made magazines on the market for a decent price and that seem to be getting decent reviews, but wasn't sure whether there's a consensus on what to choose for best performance for the money.

 
They are Taiwan produced, good quality and run fine. Do a search here and you will find pages of information.

 

 
Gotcha. I'd seen the posts on the Taiwanese drums, but from what I read it seemed like people were saying only 100-200 of those drums had been made. I came across some drums for sale recently that I thought were being advertised as Korean-production. Regardless, I'll pursue that route. Thanks!
 
 

   If you want to be a Class 2 (manufacturer) SOT, you must first have an 07 (manufacturer) FFL.
Applying for an 07 undergoes greater scrutiny by the ATF.
 
     As a Class 2 you CANNOT transfer newly manufactured machineguns to other Class 2's unless
they have a Police Letter - a letter from a Police Department requesting that the gun be demonstrated.
The ATF has really tightened up on these letters - one or two words that say or imply the wrong thing
in the letter will cause it to be denied.  I have a new manufacture M1928A1 post sample receiver that
has been sitting here for over a year because the buyer cannot get the ATF to approve the transfer
with the letters he has provided, and originally he thought it would be "no problem".
 
    If a Class 2 goes out of business or changes his license then he can transfer his post samples
to other Class 2's without the Police Letter, but thats it. 
 
Bob

 
Already am Class 2 (manufacturer); already have 07 (manufacturer) FFL. The scrutiny wasn't the 'desk-lamp-in-the-face, bad cop' interrogation people frequently make it out to be, but maybe I just had a more friendly examiner? Not interested in transferring this build to another Class 2, for time being, so I don't really care about how hard it might be for someone to get a proper demo letter for it. Regardless, very familiar with the demo-letter process. Very familiar with the 'no-letter' gun situation/process.
 
Anyway, I'm not trying to get into any sort of 'whose FFL 07/SOT 02 d*** is bigger' contest here, so my apologies if I in some way offended you; the wording of your post was just so absolute and direct in the whole "there's no way anyone can legally build a machine gun, so don't try" message that I assumed you weren't aware of how the law pertaining to that sort of thing worked. I guess maybe we both learned something here about making assumptions, eh?


Edited by TehVice, 12 February 2020 - 11:53 PM.

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#19 reconbob

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Posted 13 February 2020 - 09:00 AM

Of course if you have a Class 2 that changes everything. But if John Q. Citizen
wants to make his own machine gun, really the only practical reasonable answer is
no. It is not reasonable, in my opinion, to acquire business premises and establish
a manufacturing footprint to to be able to get an 07 FFL to enable you to apply for a
Class 2 SOT, to enable you to make a gun, and to keep the gun you have to maintain
your SOT at $500 a year and your FFL at $150 every three years.
I was not intending to be harsh in my comment and if you took offense I apologize.

Bob
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#20 ppgcowboy

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Posted 13 February 2020 - 10:21 AM

It would have been nice if you had opened with what ffl licenses you had. There are people who feel that they can turn a parts kit into a fully functional machine gun, and come to places like this for such advise. Members here try to enlighten them in order to avoid undo scrutiny of the nfa. Welcome to the boards.
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