M1A1 Thompson


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Max D. Zimmerman
July 27, 2006, 11:02 AM
I am a new kid on the block, that is interested in modifying a legally available 80% machined M1A1 Thompson Receiver to the semiautomatic fire mode, that would work with an M1A1 Parts kit that is also legally available. Any help or advice will be appericated. MDZ

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OH25shooter
July 27, 2006, 11:04 AM
First thing that comes to mind is call your local ATF office. Get the "official" scoop on the law.

harvester of sorrow
July 27, 2006, 11:12 AM
The problem that you will encounter is that your design must be approved by the BATFE as a semiautomatic that is not "readily convertible" to fully automatic fire, which will be difficult. For starters, you will need to convert the M1A1 to fire from the closed bolt, which will not be easy or cheap. A much easier alternative would be to simply buy one of the Auto Ordnance guns.

Stickjockey
July 27, 2006, 02:57 PM
In addition to the receiver stuff, if you want to use the barrel that comes with the parts kit, make sure you get the proper paperwork/tax stamps/ approval for maufacturing a Short-Barrelled Rifle. The original Thompson barrel is about 5.5" shorter than they like. That or get a new 16" barrel from Kahr/AO.

JesseL
July 27, 2006, 03:39 PM
The problem that you will encounter is that your design must be approved by the BATFE as a semiautomatic that is not "readily convertible" to fully automatic fire, which will be difficult. For starters, you will need to convert the M1A1 to fire from the closed bolt, which will not be easy or cheap. A much easier alternative would be to simply buy one of the Auto Ordnance guns.

Although it may be a good idea to clear the design with the BATFE, as long as you are only bulding it for your personal use it is not a requirement.

You will wan't to be very sure that it really isn't "readily convertible to automatic fire" in the event the BATFE takes an interest in you. I've heard of them going to some pretty absurd lengths to make the case that a gun is really a machinegun :fire: .

dfariswheel
July 27, 2006, 03:52 PM
Due to the high legal requirements, and the extreme mechanical design and manufacturing requirements, I'd strongly suggest just buying a new semi-auto Thompson carbine.

These are available set up to look like either the early 1921/28 Thompson, or the WWII M1-A1 Thompson.

These are 100% legal to own, and cost far less than trying to build something from parts that ARE NOT compatible with a legal semi-auto design.

http://www.tommygun.com/

The problem with trying to build a legal semi-auto from an 80% receiver is, the receiver is 80% a full-auto and isn't going to be readily convertible to a true semi-auto.

After doing some heavy-duty mechanical design work and getting the ATF to sign off on it, you'd need to have a high-end professional-level machine shop with a full range of lathes and milling machines to actually build it.

In other words, you can't buy an 80% receiver and a surplus full-auto parts kit and do a few simple modifications to get it to both actually work AND satisfy the ATF's demands that the gun can't be "easily converted" to full-auto.

When George Numrich designed the semi-auto Thompson gun, he said that he'd spent $100,000 designing a gun that would satisfy the Feds.

Mac Attack
July 27, 2006, 03:58 PM
Like everyone else said, just buy a semi version.

The cost of a M1A1 or 1928 Thompson are around $500 and the unfinished receiver is another $200. For around $800 you can buy a replica so the cost of doing it yourself just isn't very cost effective.

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