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Gunmachines Co. Tsmg Enhanced Performance Parts


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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?

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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

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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...
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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.
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Thought I must say that shooting my '28 with a '21 actuator, and its increased rate of fire, is more fun...
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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.
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And don't forget welding M1 bolts into M1A1 configuration. What in the hell was up with that? http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/blink.gif http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/sad.gif http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/huh.gif
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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;-)

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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.

 

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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.

 

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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.

http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/biggrin.gif All deserve a round of applause since everyone throws in from time to time. http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/laugh.gif

 

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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.
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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.

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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.

 

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Gaint, the back of the receiver of an m1/m1a1 is alot thicker than the back of a 21/28 receiver so it can take the pounding from an unretarded bolt. If you cut the ears off a blish lock the back of your 21/28 receiver will sooner or later crack and fail. Somewhere on this board is the full explaination of how and why the blish lock works. The blish lock was deleted and the receiver redesigned on m1/m1a1 to decrease the cost and manufacturing time.

Kevin

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Aurther & Kevun,

Forgive my trying to be subtle, I do know the blish lock w/ears does smooth out the action and perform a function. However, I just finished Helmers's book - in which he concedes that the blish lock was not needed by the end of the book. So - was the functiuon NECESSARY?? No.

I am aware of the reason for reducing parts counts and manufacturing steps was a time/cost savings issue. Obviously a good idea in wartime. I have not shot a M1 to compare the smoothness to a 21/28. So - probably should have kept my mouth shut until I had the first hand experience.

I was refering to many enhancements that included cuting ears off, etc. I have seen many of these parts come thru evilbay from time to time as well. I do not advocate any of these parts either. But has anyone witnessed damage to a reciever by "speeding up" a 28? Surely just putting in 21 parts won't affect it. Or no one would be buying the 21 actuator kits on ebay for over $400!

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Helmer's Epiphany that the Blish Lock was an expendable part is terrific 20/20 hindsight. The fact is a 1921/28 TSMG won't function without one. Considering all the 21/28's currently being fired utilizing this 80+ year-old design stands as a testament to the reliability of this so-called superfluous part. The 21 kits sold on ebay are not "Gunmachines" speeded up parts. These British made 21 parts are in keeping with the original specifications designed to work in either 21, or 28 TSMG.
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I, too, think the Blish lock is what sets the design of the Thompson aside from others.

 

This is kind of off point but there is an article by Capt. M. Mendenhall in the Dec 2002 SAR (Vol. 6 No. 3) about the Blish lock. His analysis indicates that not only is the Blish lock unecessary but that it does not function as intended. That is, the physical device is needed to operate the bolt/actuator combination, but the Blish principle of metallic adhesion (the heart of the concept) fails to work. To wit, cut the ears off and the gun still works. I gather there were some issues with the cases bulding because of the bolt opening too soon, however. He sums it all up by saying that, "most evidence suggests though that the Thompson...functioned in spite of their bronze..locks, not because of them. Ultimately impure at its core, the Thompson...had a heart of brass instead of a heart of gold".

 

FWIW, according to Mendenhall. I'd scan the article save for copyright....

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This has been hashed and rehashed.

 

Data; none that I know of, just word of mouth. Glen Whittenburger has a WH 28 that had the back blown out. I have written him asking for details but received no response. He is mentioned by Klodinsky (Gunmachines) in his writings and I’d bet the problem started as a result of the speed bolt, but don’t know for fact. Klodinsky mentions several guns with damaged receivers but finds no correlation with his parts- I think this wishful thinking. Obviously there was enough question to cause the cessation of manufacture.

 

While the principle of metallic adhesion is questionable in the Thompson, the fact that the Bliss lock retards the action is not. The fact that a gun will work without a certain part does not mean that it is ok (especially in the long run) to eliminate it or that it serves no function.

 

The principle of blow back firearms involves balancing the force developed by the cartridge against the ability of the action to absorb the energy produced thereby. In the 21/28 the Bliss lock is a key eliminate in absorbing some of that energy and providing a bolt velocity that is commensurate with the ability of the receiver to withstand it. If the receiver is designed to withstand an impact from a certain weight of bolt at a certain velocity, increasing the velocity (removing the Bliss lock) will impart higher energy, perhaps exceeding the design parameters of the receiver.

 

Comparisons with the M1 are not applicable. When the M1 was designed it followed the established pattern of other non locked or retarded breech guns; make the mass of the bolt large enough to absorb the force generated by the cartridge. The M1 not only has a heavier section in the receiver, the bolt is also heavier.

 

21/28= lighter bolt, Bliss lock

M1= heavy bolt & receiver

Two different designs

 

Springs have not been mentioned so far; they play a role as well. The lighter bolt assy of the ‘21 is backed up by a fairly substantial spring, the heavier ’28 assy a lighter one, and the heavier still M1 bolt by the same spring used in the ’28. Springs can be important in absorbing the energy imparted to the bolt assy and slowing the velocity, thereby reducing the impact forces on the receiver. That’s why the 27a’s have such heavy springs; they have the lightest bolts which are also un-retarded and heavy receiver sections.

 

The Bliss lock is an important part of the 21/28 system. It was well thought out by some of the best engineers around at the time and proves itself in actual use. To simply reject it as “unnecessary” out of hand is foolish at best, IMHO.

 

 

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