30 replies to this topic

[ftc3906]

Back in the late 1980's, a company known as Gunmachines sold various parts to supposedly enhance TSMG reliability and performance. Gunmachines owner also wrote a monthly column on TSMG enhancement in the now defunct Machine Gun News. The parts to enhance performance and reliability included the following: bronze Blish locks with the "ears" machined off, telescoping recoil spring guides, bolts with weight reducing cut-outs to increase the cyclic rate, recoil springs of various lengths from 10.00" to 12.00" in 0.50" increments.

My question is has this body of thought and method of TSMG enhancement been debunked or is any of it valid?

[Arthur Fliegenheimer]

I wouldn't want to buy a TSMG that has, or used, these parts. This odd compulsion to speed up the rate of fire beyond what John T. intended for his design is sure folly. If you want a submachine gun, or machine gun that fires 1200 rpm get a Mac 10, or an MG42.

[TSMG28]

PK can probably provide more engineering specifics than I can, but my recommendation is to stay very far away from these parts. Furthermore, I agree that any gun that has used them could have been subjected to significant receiver battering and could be weakened.

Both the "speed" bolt (some metal removed) and Blish lock with its ears removed have been addressed many times on this forum, and I can't remember one positive thing ever being said about them. I can definitely tell you that Tracie Hill takes a dim view of these modifications.

Roger

[The1930sRust]

Arthur and Roger are dead on. I think many of the rumours we've heard regarding receiver cracking in West Hurley's stem from the use of these. Isn't the consensus many of these parts were created to work around the reliability troubles with some of these guns? A better choice, if a gun has such a problem, is to have it brought up to factory spec by a Thompsonsmith. There is also a bit or two about these issues in the FAQ...

[Bruce L]

I've got to agree that the design seems to have proven pretty reliable over the intervening 85 years or so.
Didn't make much sense to mess with it.

[full auto 45]

The only TSMG's that I have heard of having a problem were the ones that had these "performance part" installed in them. Just like a car, keep it original and it works best. All my guns are original and stay that way. Except the AR and little thing like the barrel and such. But don't mess with the bolt and weight of it.

[The1930sRust]

Thought I must say that shooting my '28 with a '21 actuator, and its increased rate of fire, is more fun...

[full auto 45]

Chris, I did a timed test with Brickyard a couple months ago. He has a 21 kit and my stock WH 28 ran identical tmes to it. Yes I know it is hard to believe but even he couldn't believe it! We did it a couple of times in the onslought of the attacking terrorist pumpkins, but it was true. I fired a 30 round clip and so did he and both started and ended in nano-seconds of each. Ask CJ he will tell you. His did seem smoother than mine but ran at same times.

[Gunner]

Full Auto,

I wonder that's possible? Seems like, by definition, the 21 kit would cause you to run out of ammo sooner.

[Waffen Und Bier]

And don't forget welding M1 bolts into M1A1 configuration. What in the hell was up with that?

[The1930sRust]

Mike:
Hmmm. Lube differences? Spring tensions? Mine is markedly faster with the 21 kit. I've timed the differences with the video camera and, though far from quantitative, the audio difference alone is significant. CJ, just cut the ears off the Blich lock;-)

[PK.]

At 750 rpm it takes 2.4 seconds to empty a XXX mag. At 900 rpm it takes 1.99 seconds. I must submit that if you started ¼ of a second sooner than Brickyard and he finished ¼ of a second before you did, it would not be noticeable.

That said, different guns run at different rates. I have a 28 in the shop that runs almost as fast as a 21 for no apparent reason. I haven’t taken the time to dope out why yet, but it stands to reason that certain combinations of components will run faster and others slower. It’s called tolerance.

When shooting the two guns (21 & 28) there is a noticeable difference however.

On the “performance parts” question; I feel strongly that the parts and practices advocated and sold in former days are pure poison to the Thompson and should be avoided. If the gun is set up as a 1921 model it is plenty fast and within the design parameters intended for it.

[SecondAmend]

If the memory of my 30+ year old engineering training is still intact, the action is going to run (and hence set the firing rate) in a rough approximation of a so-called "simple harmonic oscillator." The means the firing rate will be approximately proportional to the square root of a combination of the mass of the reciprocating components divided by the spring constant of the recoil spring. Since the spring constant is approximately the force that causes the travel of the reciprocating parts divided by the amount of travel, the firing rate is roughly proportional to the square root of the mass of the bolt/actuator multiplied by the bolt/actuator displacement and divided by the force generated by the ammo.

Decrease the mass or displacement, or increase the spring stiffness or the ammo force and the firing rate goes up, reverse of the same and the rate goes down.

Further, the force generated by the ammo has to be great enough to work the action with a reasonable variety of ammo without bashing out the back of the receiver (i.e., the impulse of the fired round has to be equal to or greater than the momentum of the reciprocating parts). Hence, the component sizes fall within a range of generally acceptable size, weight, spring force, etc. plus a buffer is needed to ensure that the ammo force values that exceed the usual tolerances are accommodated. Go out of the design range with any part in any direction and trouble results. Eichoff and Payne, and the Savage engineers were all very good engineers. Stay with what they put in the original packages.

Comment and/or corrections are welcome.

[full auto 45]

SecondAmend- Don't talk like that again! My head damn near exploded!

[ThompsonCrazy]

Wow... That education was money well spent. I wish I knew what you were talking about but all in all I can read through the lines....I think? I would think that he difference in the mass from a 21 to 28 would cause a different elapsed time from case extraction to round firing. Glad there are board members as such that have this knowledge. I must say that collectively this bunch can analytically discuss, diagnose and repair the TSMG with personality.
All deserve a round of applause since everyone throws in from time to time.

[Roland, Headless Thompson Gunner]

Ditto what SecondAmend said

[Arthur Fliegenheimer]

Kudos go to Philip P. Quayle, the mathematical scientist whom John Thompson hired to design the actuator for the 1928 Navy. Somehow Oscar Payne became credited with this innovation. When Savage decided to go into the TSMG business, it is Quayle's ingenious "slowed down" design feature they chose to incorporate into their 1928A1 version.

[Sgt]

SecondAmend--
You brought back a lot of unpleasant memories of my days in engineering school. I squeaked by in Dynamics and took Thermodynamics three times. Enjoyed your cycling analysis, just the same.

[giantpanda4]

Second Amendment,
I know I forgot all of what you said when I got my two engineering degrees. It's easy to do when you don't use it. But, for alluded to a damn good point - why does the speeded up action cause more wear and tear on the reciever? The input force is the same (same ammo)! So - the reaction force must me the same, right? I think what is going on here deals with energy- same force, less time, more energy. Or something like that - maybe 8 years ofo college went down the drain already.
Does anyone (PK??) have any data (picture or story) of a reciever that failed - especially due to being "speeded up"? And why it failed (history of use/abuse)?
I think we all know that the blish lock was NOT a requirement in the design of the TSMG - Gen. Thompson would not agree, but the M1s work fine without them. If there is an additional problem with just "cutting the ears off", I would like to know why.

[Arthur Fliegenheimer]

Giant,
Are you advocating turning 1921/28 Blish Locks into Vincent Van Gogh's? The reason the M1 SMG's work without the Blish design is because they are as different from a 1921/28 TSMG as an M3 Grease Gun is.