Interesting XXX Mag with Round Counter

[MauserMatt]

Came across this magazine the other day. I looked through the magazine reference guide here on the forum, but didn't see any mention of such a thing. So I assume it's either a field modified magazine, or something that a civilian owner may have done in the 75 years since it's military service.

 

 

 

[bug]

Matt, I'd say home mod. Is that a crack between 20 and 30 rnd cut?

 

Bob D

[john]

Looks like a weld....look at the spine too.

May be a very early 30 round homemade stick?

Just a guess that doesn't make sense as why not make a 40 from two 20's?

Edited October 4, 2020 by john

[TSMG28]

Matt,

 

What you have there is one of the prototype 30-round mags that Crosby made up from two 20-round Crosby mags for consideration of the Armored Force Board in Fort Knox. The design was tested on 6 December 1941 and recommended for adoption. The witness slots were not adopted, but the 30-round design was, and subsequently made in the millions by four different manufacturers, including Crosby, who gave the government the rights to the design. See American Thunder III, pages 239-240, and TUTB, pages 605-606, for more details.

 

If you ever want to sell this, I am very interested.

 

Roger

[Frank Iannamico]

Those magazines has been covered in most of the available books on the Thompson. Pretty rare magazine!

Image and text from AT3.

 

The Crosby Company was a prime contractor for both the fifty-round drums and twenty-round magazines for the Thompson. During the war, Crosby engineers developed the thirty-round magazine. Because its efficiency, the thirty-round, magazine ultimately replaced both the fifty-round drum and twenty-round box magazine.

Crosby’s prototype magazine was constructed using two existing twenty-round magazines. To increase the capacity, a 2-3/8-inch extension was welded to the bottom of a standard twenty-round magazine. The extension expanded the capacity to thirty-rounds. A newly designed, longer spring was also required. Elongated slots were cut into the side of the magazine to enable the operator of the weapon to see at a glance the total number of rounds remaining in the magazine. The slots were replaced by circular holes in production magazines. Crosby granted the U.S. government all rights to the thirty-round magazine: “As the licensor of the thirty-round, Crosby granted nonexclusive, irrevocable, nontransferable and royalty-free rights to the United States Government, to use and manufacture or have manufactured for government purposes in plant’s other than Crosby’s this Crosby invention.”

There were several tests conducted by various U.S. Army boards to compare the thirty and forty- round magazines as possible replacements for the twenty-round box magazine and fifty-round drum magazine. On 6 December 1941, the Armored Force Board at Fort Knox, Kentucky field tested the thirty and forty-round magazines. A total of 2000 rounds were fired. The test results revealed “Both types functioned well mechanically.”

[Bridgeport28A1]

MauserMatt, thanks for posting the photos.

[MauserMatt]

Oh wow, thank you gentlemen for the information! Especially from Mr. Iannamico himself!

 

I do have a copy of American Thunder III, just didn't even think to check it as I never would have thought this to be a prototype.

 

Here's a couple more pictures. I do see where the donor magazine was chopped as you can see "THE" still intact. Crazy this was just thrown in the mix with a bunch of other magazines and I happened to come across it.

 

 

 

[Frank Iannamico]

That was quite a find of a rare magazine, Tracie has one in his collection the only other one I know of.

 

I went to the importers when the '28 TSMG Russian kits came in. There was two crates with 3k magazines in them. I spent two weeks unwrapping/checking magazines all brand new.

I found 3 or 4 unmarked and 1 patent date mag. The thrill of the hunt!

 

Frank

[Mike Hammer]

Frank you mentioned a 40rd mag was tested as well. I don't suppose any of those mags has ever surfaced? A 40rd stick mag would be interesting to try.....

[DFisch]

Someone on Youtube has a home made 50-rd box mag...

 

www.youtube.com/watch?v=9spzqY4PxOM

Edited October 5, 2020 by DFisch

[TSMG28]

The 40 round mag was just two 20s welded together on their face. See the pic Frank included above. You still had to change mags at the end of 20 by flipping them around. The 40 round UD42 mag worked the same way.

 

We have seen a number of battle pics showing that soldiers had taped two or more mags together, but many of those pics show the 30-round mags being used.

 

The cobbled-together very long 50 round mag used the same concept that Crosby used to make the 30.

[john]

Frank, I bought a few parts kits from the same source as you. They came with a belt, a 5 cell pouche and mags. I did find a plain unmarked mag as well as a patent dated MSCO marked mag in the mix.

Lightning struck twice, I guess!

Edited October 6, 2020 by john

[Frank Iannamico]

Frank you mentioned a 40rd mag was tested as well. I don't suppose any of those mags has ever surfaced? A 40rd stick mag would be interesting to try.....

Nope, never saw a 40 round TSMG mag as depicted, there are UD42 '40s but no Thompson.

The problem with the design was the possibility that the inverted magazine would be exposed to dirt etc. If the shooter was in a prone position.

[Ivan]

Actually the UD42 magazine holds 25 rounds so the back to back UD42 mags should be considered 50 rounders.