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Gunmachines Co. Tsmg Enhanced Performance Parts


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#21 Kevin

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Posted 23 November 2003 - 12:17 PM

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.
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#22 giantpanda4

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Posted 23 November 2003 - 11:57 PM

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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#23 Arthur Fliegenheimer

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Posted 24 November 2003 - 10:37 AM

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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#24 The1930sRust

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Posted 24 November 2003 - 11:40 AM

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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#25 PK.

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Posted 24 November 2003 - 12:49 PM

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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#26 Arthur Fliegenheimer

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Posted 24 November 2003 - 03:08 PM

Pk,
Thank you again for explaining the engineering science behind the Blish Principle. It is indeed tedious that this topic, covered ad nauseum, still rears its ugly head. Maybe this commonly known fact should be a banner flashing across the top of the screen on this board.

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#27 TAB

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Posted 24 November 2003 - 03:50 PM

Despite it being a moot point perhaps, as i will never likely afford a real Thompson, I found PK's explanation excellent. Particularly as it really speaks too more than just the issue at hand.

It is rare to see the physics so well and completely presented with neither embellishment nor vague allusion.
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#28 gijive

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Posted 24 November 2003 - 04:05 PM

Paul,

Excellent post regarding the Blish lock. As stated, it is an integral part of the design of the 1921/28 gun. It prevents premature ignition, absorbs recoil and functions as it was supposed to. Your right, elimintaing a portion of it doesn't mean it isn't necessary for the proper function of the 1921/28 model.

Good job!
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#29 SecondAmend

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Posted 24 November 2003 - 05:58 PM

Anyone have access to some good simulation software?

Nowdays the engineers model stuff like this and try it out by computer before putting the milling machine to the metal block.

One could readily do a series of sensitivity analyses to see how much the ammo force can vary, how much the spring rate can vary, what the actuator/bolt mass range must be, when the Blish lock does what, and so on.

Plus, we could then not only discuss whether or not the Blish lock does anything, we could also discuss what is wrong with the computer model.


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#30 giantpanda4

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Posted 24 November 2003 - 10:47 PM

PK,
Thanks for the excellent clarification. I do believe we are on the same page - my noting the blish lock is not necessary should have been referring to whether or not the principle of metallic adhesion is a viable one. Thank again.

As far as simulation... I prefer to stay working in the real world! That's why I work on the actual cars/parts at work - not hours and hourson a tube (I'm told I can't even spell komputer...). I am sure it is a lot more fun to shoot a lot and record the data that way!


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#31 Bisley45

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Posted 25 November 2003 - 08:45 AM

giantpanda4

28's are thinner at the rear end, without the blish lock to slow it down you beat the rear or the recever to death. The M1 has a LOT more metal and is contoured diferently and designed to take that pounding where the back of the 28 is opened up to take the oiler right there.

BB
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