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Old October 24, 2010, 11:50 PM   #1
chris in va
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45acp subgun?

I don't pretend to know much about FA firearms, but this one has me stumped.

I saw a gentleman shooting what looked like a FA MAC 10, but to my surprise all I found was 45acp shells under the table. So my first question is...what is it?

Second question, why would it bulge the brass like this?



I had little trouble resizing it back to shape, but curious why it bulged so far up the case. The thing was really fast, like an UZI.
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Old October 25, 2010, 01:50 AM   #2
RAnb
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I will hazard a guess. The bulge may have been caused by high pressure upon extraction. If the bolt or spring were too light, it is possible that it was extracting too early and causing the bulge.

This is only an educated guess on my part. I'm not sure what the M10's fired brass typically looks like.

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Old October 25, 2010, 06:12 AM   #3
1911rocks
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MACs are a beast on brass

That's more or less normal. The springs need replaced about every 6000rds. The Ingram or M10 (commonly referred to a "MAC") was available in 9mm & 45acp. The latter was quite popular due to the effectiveness of suppression. The 45acp variant was ~1100rds/min weapon. This was part of the advantage of an M10. Ingram designed it as an ambush/counter-ambush weapon. It's not a "precision" tool. It was a "get them all, let God sort it out" tool. There were several suppressors available. The Sionics weighed over a pound. Heavy by today standards. There was an M11 in 380acp. It was a bit smaller than the M10. In the latter years there was an elongated model of the M11 in 9mm. If you own a M10 you don't reload. Do the math, the magazines hold 40rds You will empty one in 2.4sec. Unless you own a Star machine you'll be "yanking a handle" for a long time. Before 1986 the MAC could be purchased for under $300.00.
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Old October 25, 2010, 07:08 AM   #4
chris in va
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Thank you very much. It was definitely fast, so probably why the case didn't have time to reduce pressure before extraction.
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Old October 25, 2010, 02:33 PM   #5
demigod
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Those junk machine pistols fire from an open bolt I think. I remember seeing some dude shooting one out in the sticks. He said I could have his brass, but it was all bulged out like that. I'm not sure if it's from firing slightly early (out of battery) or if they just have really sloppy chambers to get them to run.
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Old October 25, 2010, 03:23 PM   #6
Skans
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Those junk machine pistols fire from an open bolt I think.......
Those M10's are actually very rugged. They are also modular and parts/barrels, etc. are easy to replace. There's nothing wrong with an open bolt sub-gun, both UZI and Thompsons are made with open bolts. In fact, open bolt design has some distinct advantages in sub-gun design. It keeps the barrel cooler and doesn't let a locked round "cook-off" in the chamber. They are better designed to be short range bullet-hoses.
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Old October 25, 2010, 05:36 PM   #7
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Sub Guns

There are a few exceptions (MP5), but, most sub guns fire from an open bolt. The primary reason for the bulge is attributed to those guns being blowback guns. As to Junk I've used an Ingram for the purpose they were designed for. They are perfect for that application. The last gun I want in battle field environment. The first gun I want in a small room with a bunch of bad guys. The ultimate Industrial Ed project was the M3 (grease gun-only the barrel and the FCG was machined) a lazy 450rds/min. They fire from a big massive open bolt witha long stroke. They won't eat you out of house and home either. These were designed to be thrown away. Even the incredibly designed and machined Thompson Submachinegun Model 1923 was an Open Bolt, Blow Back design.
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Old October 26, 2010, 09:41 AM   #8
demigod
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I guess, Skans. To me though.... any gun that kicks out a cartridge looking like that is junk. And I understand the bennies of open bolt. But on a stick mag feed sub gun... I don't see it as necessary.
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Old October 26, 2010, 09:54 AM   #9
Skans
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I guess, Skans. To me though.... any gun that kicks out a cartridge looking like that is junk.
If you're reloading to feed the beast, I can certainly understand the drawback to owning one of these; you won't get as much milage out of the brass. But, if the gun does what it is supposed to do, what difference does it matter what the spent shell looks like?

Last edited by Skans; October 26, 2010 at 11:12 AM.
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Old October 26, 2010, 02:31 PM   #10
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The MAC's are a good entry level subgun that are a hoot to shoot suppressed.
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Old October 26, 2010, 03:13 PM   #11
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Subguns in General

It may be a hard pill to swallow, but these subguns, and machineguns for that matter, weren't designed for the hobbyist. They were design for a tactical employment, not for an afternoon outing. Cost of ammo and reloading means zip. In the case of an Ingram, they were designed to deliver massive amounts of lead in a CQB situation. Ambush/Counter-ambush. When Ingrams were employed for Ambush in SE Asia the assumption was everyone in front of the gun was a BG. In Counter-Ambush the same held true. Oh, and they are a joy with a can, scary as a Liberal without one. The M11 in .380 with a can is BIG fun, pricey, but big fun.
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Old October 26, 2010, 03:14 PM   #12
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The reason for an open bolt is for cooling. Thompsons and other full autos are most effective when fired in 3 to 5 shot bursts. The fact the bolt remains open helps to keep the barrel cool. The Thompson has cooling fins in it's barrel so that plus the open bolt make it a more effective weapon.

When the Thompson was invented they did lot of research and testing to find the best caliber and brass length.

The .45 ACP was chosen because of (I forget the exact term coefficient of extraction). They also included a Blish Lock to delay the extraction from the chamber. There are a lot of factors that go into the design and to really understand the process you need to get s book on the subject
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Old October 26, 2010, 10:24 PM   #13
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An UZI is one of the slowest machineguns made, the M10 is one of the fastest.
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Old October 27, 2010, 10:29 AM   #14
Mike Irwin
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"The reason for an open bolt is for cooling."

Yep. With an automatic weapon you can heat the action up quickly enough to cook off rounds, and the firing from an open bolt helps prevent that.

There have been numerous full/semi autos over the years (primarily ones that fire rifle cartridges) that fire from an open bolt during automatic fire, but when switched to semi-automatic mode fire from a closed bolt.

The Johnson Light Machine gun comes immediately to mind.
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Old October 30, 2010, 11:49 AM   #15
dajowi
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The Mac-10 .45 I've got certainly couldn't be described as "junk." After the 2.4 second 40 round burst, I can use it as a club.
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Old October 30, 2010, 12:40 PM   #16
James K
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An open bolt SMG design does cool better, but that is not its main advantage. By using an open bolt, the gun is set up so that it can use advanced primer ignition (API), touching off the primer just BEFORE the bolt fully closes. That means the backward pressure is fighting the momentum of the forward-moving bolt as well as its mass. And that means the bolt can be much lighter and use much lighter springs than if the gun is made to fire from a closed bolt.

Anyone who has fired both the TSMG and the current semi-auto version will know exactly what I am talking about.

There was actually no experimentation with other calibers during the design of the TSMG, the earlier .30-'06 auto rifle having been abandoned. The .45 ACP was chosen simply because it was the U.S. service cartridge and the market was intended to be the U.S. military. Early advertisments say the gun was available in ".22, .30., 38., and .45", but only the .22 (a conversion unit) was produced. I have seen no indication which .30 or .38 cartridges were meant.

Later, in 1926, guns were made in the UK by BSA in 9mm Parabellum, but those, while internally like the standard Thompson, had a different profile.

(Those bulged cases seem to be the result of an ovesize chamber, not the gun opening too soon.)

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Last edited by James K; October 30, 2010 at 01:05 PM.
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Old October 30, 2010, 10:09 PM   #17
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The Sten is also an open bolt, the only thing I did not like about shooting it was the momentum of the bolt going fwd on the first round. How bad is it on a Mac?
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Old November 21, 2010, 11:14 AM   #18
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In theory, open bolt subguns like Stens, MACs, and others with fixed firing pins are designed to detonate the round while the bolt is still traveling forward and before the cartridge is fully seated in the chamber. The forward inertia of the rather weighty bolt is supposed to counteract the rearward thrust of the detonating cartridge, allowing it to finish seating, then pushing the bolt rearward via residual gas pressure. (Or at least that's the way it was explained to me.) The bulged brass you saw was most likely the result of a weak recoil spring, allowing premature unseating of the cartridge case after detonation.
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Old November 22, 2010, 09:21 AM   #19
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How bad is it on a Mac?
Don't expect to hit anywhere near where you thought you were aiming with the first round. That's what the other 29 rounds are for.

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Old November 23, 2010, 04:21 PM   #20
jheitertusa
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Off topic a bit, but I SO want to buy a MAC 11/9 and get in to the NFA fun...

Maybe if I can convince my wife since it is safer than the motorcycle I have been wanting....and cheaper....hmmm...
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