Posted 25 November 2003 - 02:26 PM
The system of all 3 is to an approximation a mass on a spring, with a retarding force( friction or friction/blish lock). A damped oscillator. When the trigger is squeezed and the safety is off, it becomes an oscillator driven by periodic forcing functions, the base of the cartridge pushing on the bolt after the explosion and the reaction force at the rear of the action as well. Right?
Is it possible to get resonance problems?
The natural frequency is the square root of k/m. Going from the '21 to the M1 you increased the mass m of the bolt, but you also decreased the k of the spring, the 'stiffness', thus lowering this natural frequency. Does this effect the ROF? I know nothing of mg theory, sub or otherwise.
oh look, it's time for lunch...
Posted 25 November 2003 - 04:27 PM
It was PK's explanation yesterday that got me thinking. At the risk of being rude, that doesn't happen all that often. Doesn't mean I didn't in the end ask a dumb question, but I've answered my share of them without mocking the person.
Not that i didn't get a laugh out of the story of the klansman.
Posted 25 November 2003 - 05:17 PM
PS A least your question was addressed to people who may understand the question...
Posted 25 November 2003 - 05:57 PM
Posted 25 November 2003 - 08:17 PM
Posted 25 November 2003 - 08:36 PM
That makes sense. When I first read it I was reminded of music for some reason, and could not make the connection to guns. Just like you get different tones out of different size cymbals, you would get a different "resonance" with a heavier or lighter bolt.
It seems to me the discussion on the 27A's recoil springs would apply here. If you lowered the springs tension, you would get a faster bolt action. So fast in fact that the bolt slamming into the rear of the reciever could set up some bad "resonance". BUT, if you managed to somehow increase the weight of the bolt, you would counteract the effect of the lightened springs.
Or something like that...
Now I just need to know what the "k" and the "m" stands for in the phrase "square root of k/m"...
Posted 25 November 2003 - 09:28 PM
The point is that by changing springs or bolt weights, you are playing with factors that are part of a whole, if that makes sense. The 'damping' is important too- I'm guessing part of the effective purpose of the blish lock was just that, as many screen doors have springs such that the door will close at a reasonable rate, but if you try to slam it, it will resist. But I am guessing.
The resonance is as MkVII pointed out, if you feed energy into such a system in 'tune' with the system, you get a big bang for your buck, even in a real system where there are frictional losses... The Tacoma Narrows Bridge is the classic example of what can happen...and even rebuilt I didn't care for driving over it entirely.
Anyway, what does determine the ROF of an automatic weapon?
Posted 25 November 2003 - 10:15 PM
If you ask me, why fix it if it aint broke....
Posted 26 November 2003 - 12:03 AM
Different than damping altogether then, though once it releases you still have the same basic system. I'm sorry, I should have read a bit on it first. I see its been discussed before. More than some want . It is allowing energy to be bled away that would otherwise go into the bolt velocity and spring compression, but it is not continuous, just an initial retardation.
I now have even more questions, but enough... Things are only simple when I misunderstand how they work.
Posted 26 November 2003 - 02:01 AM
Posted 27 November 2003 - 12:01 PM
At the front end is the bronze lock with quite a bit of contact area with the heavy receiver.
The bolt basically runs on a thin cushion of oil, another excellent medium for dampening vibration and bleeding it off to the heavy receiver.
BUT the vibration is still present to a small degree.
Those of you who have several thousand rounds through your Thompsons with the same spring pilot, pull the pilot out and look at it carefully. My '28 pilot (a Savage part) shows wear based on either a fairly high frequency oscillation near the front of the pilot OR maybe based on spring twisting as the spring is compressed. Wear rings a bit closer than 1/16" extend back about 1-1/2 inches along the pilot........
I can't see any other evidence of chattering or vibration anywhere else in the gun (an A.O. Bridgeport) but I'm no expert on harmonics.....
I do know that harmonics plays a significant role in accuracy using various velocities, bullet weights and velocities (been handloading varmint gun ammo for many years) so sometimes it must be considered, however, I don't think it really matters much in the operation of a Thompson Subgun. After all, I have spare spring pilots and springs, and they are cheap.
BUT MAYBE this is why some ammo runs better than others in various guns......
food for thought?
Posted 27 November 2003 - 06:56 PM
When I hear stories of bashed up recievers, and PK has mentioned the Gunmachines folks may have had some damage to their recievers when they were playing/developing their parts (please correct this, PK!) usually the reciever damage is secondary to what may have actually failed. As an example, I have many go kart race engines with windows in the side of the block. Was usually caused by oil dippers failing at 7000 rpm, then rods, then you just have a pile of scrap metal.
I would love to still hear more stories of how parts (especially recievers) are "failing". Usually an autospy will determine what really failed first.
What would you think if a test rig was devised to determine forces at the base of the reciever? Then we could do a fatigue calculation on the reciever. A strain-gaged block of metal with the insides machined out to accept a factory bolt system and barrel. Of course you need some sort of trigger, too.
Honest, ATFman! It is just a test rig!
Gotta go get seconds....
Posted 27 November 2003 - 09:14 PM
If you read up on the gun itself the blish lock principle is basically a hoax! I mean it DOES work but not on all cartridges in all occasions THE only cartridge that actually worked in all of the tests was the pistol caliber cartridges, anything with super velocity was just not feasibly actually if I am not mistaken Thompson wanted to have rifle caliber cartridges on his trench broom, 30.06
Maybe I am wrong, but I have spent 12 years of my life designing and making springs from Heavy trucks to patriot Missiles to nuclear submarines all of the factors come into play, but in this instance I donít think harmonics, and vibration are a major concern
Just my silly opinion