Are Thompson Magazines "Semi" and "GI"?

[CapnMac]

Was afoot elsewhere, and a person asked about the price value for Thompson stick mags.
I'm reading along and there's a person who is certain that magazine latch holes for "semi-auto" Thompsons are, A, larger, and B, about 0.100 lower on the receiver.

Now, I've heard of modifying various mags to other uses, but not guide-rail tommys.

Am I crazy (well, that'd rather past debating) or what?

 

[AlexanderA]

That is correct. The upper receivers on semiauto Thompsons are 1/10 inch shorter in height, so that full-auto parts won't fit in them. Now, the mag catch is on the lower receiver (grip frame). That means that a standard (full auto) Thompson magazine will sit too high relative to the upper receiver (actually it won't fit at all, because of the location of the locking hole). There are two solutions to this problem, if you have a semiautomatic Thompson. The first is to use a dedicated semiautomatic magazine made by Kahr. These are pricey and hard to find. The second solution is to take a Dremel tool to a standard magazine, and elongate the locking hole 1/10 of an inch upwards (that way it will sit lower relative to the upper receiver). Of course, this ruins it for future use with a full-auto Thompson.

These modified magazines make their way back to commercial channels, and are often passed off as being for original Thompsons. Buyer beware.

You can buy military surplus Thompson magazines for about $30 apiece (in like-new condition). Kahr semiauto magazines are about twice that. So you see the incentive for going to work with a Dremel tool.

 

[CapnMac]

Yeah, after wandering various board last night, I confirmed that.
Also, that most sellers of magazines do not appear to have a clue.
I did note that the general speculation was that the magazine change was to sell Kahr mags and no other reason. Also, that Kahr magazines are not worth their price, too.

Rather a lot of tinfoil hattery pretty quick on "compromises made in AO/Kahr's purchace of the "west hurley" tooling from Numrich. The dim is strong, and will shout down all factshaming.

 

[Carl N. Brown]

AutoOrdnance had to make the semi-auto receivers 0.1" shorter in heighth for ATF approval of the semi-auto design to prevent the receivers being used with GI parts kits to make full auto Thompsons. It's like the ATF rule that a semi-auto Sten has to use a thicker receiver tube and a shaved bolt: to prevent use of the mil surp parts kits.

AO Numrich (pre-AO Kahr) used surplus magazine catches, extractors, stocks and other small parts (post WWII Numrich bought the original Thompson Auto Ordnance's inevntory and name and sold a few full-autos in the 1950s). For the semi-auto it was easier to cut 0.1" off the top of the hole in the sheet metal magazine than cut the magazine catches. Some owners did install modified magazine catches to use unaltered Thompson magazines (which really makes sense if you also own a NFA registered Thompson.) Me, I have altered magazines my TM1, four 30rd, four 20rd, that I bought when they were $12 to $14 at the gun shows. If I knew then how the magazines have gone up in value since, I would have filed the catch down myself!!!

 

[AlexanderA]

Also, that most sellers of magazines do not appear to have a clue.

There was a seller at the military vehicle show at Aberdeen, Maryland, 3 or 4 years ago, that had a whole pile of surplus Thompson magazines. Rummaging through the pile, I found one that appeared not as well made as the others, and the seller let me have it for less. Only later did I realize it was a semiauto Kahr magazine, because of the location of the locking hole. I guess I got a bargain, but I really have no use for it.

AO Numrich (pre-AO Kahr) used surplus magazine catches, extractors, stocks and other small parts (post WWII Numrich bought the original Thompson Auto Ordnance's inventory and name and sold a few full-autos in the 1950s).

I've owned both an "xNAC" full-auto Thompson (from Numrich in the immediate postwar period using leftover inventory), as well as a full-auto "West Hurley" (made by Numrich in the early 1980's). The "xNAC" was pretty much up to wartime standards, but the "West Hurley," frankly, was terrible. All of these, now, are worth considerable money because of the Hughes Amendment. It's to the point where you are buying the paperwork more than the gun itself. Most owners of "West Hurley" guns have had them reworked (such as by welding and re-machining the Blish locking slots), so now they're OK. This expensive work is economically feasible only because of the artificially increased value.

The importation of Russian parts sets (from Lend-Lease guns) a few years ago allowed the owners of "West Hurley" guns to replace almost every part of their guns except the receivers.

 

[Ryanxia]

Yeah it's too bad people ruin original surplus parts for the Kahr Thompson of all things. I had a semi-auto Thompson and hated it. Almost 50 lbs to cock it, no joke. I'm a big dude but with that little knob I had to put the butt stock on my thigh and use both hands to cock it. A couple years later I tried someone else's and it wasn't as bad but still not something I consider decent.

 

[AlexanderA]

Yeah it's too bad people ruin original surplus parts for the Kahr Thompson of all things. I had a semi-auto Thompson and hated it. Almost 50 lbs to cock it, no joke. I'm a big dude but with that little knob I had to put the butt stock on my thigh and use both hands to cock it. A couple years later I tried someone else's and it wasn't as bad but still not something I consider decent.

I suspect that some people buy semiauto Thompsons not to shoot them, but to own a piece of history (now that real ones are so expensive, and also depending on state law). And, once SBR'ed, they don't make a bad display piece.

However, if you just want a display piece, you're better off buying an 80% receiver from Philadelphia Ordnance or Doug Richardson and assembling a dummy gun with a parts kit. This will end up costing you more than a Kahr semiauto, but at least you (or your heirs) might complete it into a real gun if and when the Hughes Amendment is ever repealed. (That will probably remain a theoretical possibility only.)