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


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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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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
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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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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
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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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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
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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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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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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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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.

  • Upvote 1
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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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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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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
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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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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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Related to the tangent topic of legality, what is the case for an NFA gun that was registered (whether demilled or functional) but current possessor doesn't have paperwork? Is there a way to change the registration of such an item to the current possessor?

 

Could see this fairly common as people might become infirmed/pass away without transferring

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This situation has certainly occurred in the past. I believe it is most common with the older dewats, many times where the original owner or heirs had no idea any paperwork was required for ownership, much less transfer. It is my understanding if the properly registered weapon stays with the Executor or the family, i.e., spouse or sibling, the ATF is very amenable to transferring the NFA weapon to an eligible recipient. Once the weapon leaves the control of the registered owner or lawful heirs of the registered owner, the situation becomes much more problematic and often results in forfeiture.

 

I post this just as general information. I am sure there are much more knowledgeable sources for this subject on the forum. Please do not take the above post as an absolute. Each situation is different!

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Yes, this came up a lot some years ago when the greatest generation vets started

passing away. back in the 1970's when I first had my gun shop it seemed like every

month or two somebody walked in the shop and wanted to know what to do with the

Grease gun, MP-40, Thompson, MP-44, etc. etc. Dad brought back in his dufflebag.

This happened so often that my opinion then (and now) is that there are as many -

or more - unregistered MG's out there than there are registered MG's.

 

My belief at the time was that if you contacted the ATF about an MG for which you do

not have the registration paper, that the ATF would confiscate the gun and make no effort

to check and see if it was on the registry.

This was why just about all of these people thought that the best thing to

do was to do nothing and keep ATF out of it.

 

The only people that contacted ATF were survivors or executors who were afraid of

guns and didn't want guns in the house.

 

I am sure others have had different experiences and will offer different opinions.

 

Bob

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