Automatic Rifle Operation Methods

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KW

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Well it's a slow day in the office today so help me stay awake! :)

What different gas/bolt systems exist for semi-auto rifles?

We've got our direct gas ala AR-15. Are there any other rifles that use this system?

We've got the delayed blowback roller locking HK's. My understanding is that the MP45 was the originator of this system. I've also read that the FAMAS uses a similar system.

Lastly we have our gas piston/op-rod setups. AK, M1 etc. Are all of these setups basically similar, or are there big differences in their designs?

Am I missing any other systems?
 
Well, going back a while, there were the Pedersen toggle, the Thompson Blish "lock" and the Garand primer setback systems, plus Johnson military and Browning/Remington commercial moving barrel recoil operation.
SIG built some rifles that were roller LOCKED, with a gas piston moving the bolt carrier instead of inertia.
Then you get into how the breech locks up, whether with a rotating bolt, tipping bolt, or separate locking block.
 
Jim hit it on the nose.

I've got rifles and shotguns that operate on the long-recoil principle, where the barrel, bolt, and bolt carrier move backwards under recoil, then the barrel is allowed to run forward and trip a release. This releases the bolt and bolt carrier to strip a fresh round from the magazine and chamber it, completing lockup in battery. Examples include the Browning Auto-5 shotgun, Remington Model 8 and 81, and I *believe* the M1941 Johnson rifle.

One of the more unusual gas systems is the one found in the Czech VZ-52 SHE rifle. The gas piston is actually a sleeve around the barrel, and the oprod is a semicircular piece of stamped steel, the whole thing fitting rather neatly under the handguard. ;)

Then there was the Browning/Colt Model 1895 "Potato Digger" machine gun, which figured prominently in the Boxer Rebellion. If you were shooting from low cover, you could either dig a trench underneath the muzzle, or let the gun do it for you. :D
 
The Johnson rifle and machinegun are short recoil, as opposed to the long recoil of the Browning Auto 5 and the Browning-designed Remington 8/81.

The medium stroke piston (Saive system) is one of the most common, being used in the Tokarev, the German G/K43, the FN 49, the FAL and the AR-18/180.

AFAIK, the short stroke piston was used in only one production rifle, the U.S. M1 carbine, though there were a few experimental imitations. The U.S. M1 rifle (Garand) uses a long stroke gas piston, which has not been used elsewhere except in copies. The German G.41M and G.41W used a conical gas trap with the piston around the barrel and a long operating rod but were, nonetheless, medium stroke.

Direct gas impingement was used in the Swedish Ljungmann 42b, the French Mle. 40/44/49 semi-autos, and the U.S. AR-10 and AR-15/M16; the Remington Model 740 and its successors use a variation of gas impingement acting on a gas cup and operating rod.

In many cases, the principle of operation, such as gas piston, and the locking system are not absolutely tied together. The gas piston of the M1 rifle could have been used to operate a tipping block; the medium stroke piston of the FAL could have been used to operate a turning bolt. For that reason, it is usual to describe a system not only by the way its operation is initiated, but also by the way in which the locking is effected.

Jim
 
The FAMAS is a retarded blowback like most HKs (the new G36 excepted) but the method of retarding the bolt opening is different - it doesn't use the rollers.

Tony Williams: Military gun and ammunition website and Discussion forum
 
I've wondered how the extractor works in a tilting bolt design. Of course the case has to be pulled straight back out of the chamber, and the extractor must stay engaged to the case head, so does the extractor tilt as well, in the opposite direction from the bolt?
 
Degtyarev

How about the Degtaryev with the primer actuated unlocking
Click to expand...
all Degtyarev designs (DP DT and DA 7.62x54R machine guns, DShK 12.7mm HMG, and 7.62x39 RPD LMG) were gas operated guns with Friberg-Kjellmann locking, where two flaps were extended sideways from the bolt to lock into recesses in receiver wall. The firing pin has been used to force teh flaps outwards upon the firing, as all those guns were open-bolt designs, and this system provided valuable safety measure - the firing pin cannot go forward unless the flaps are out and locked the bolt. To unlock, the gas piston pushed the bolt carrier rearwards, and this forced the flaps into the bolt, out of lock.
you can see the pic of the Degtyarev bolt here: http://world.guns.ru/machine/mg34-e.htm

there vere few primer actuating designs, including equally unsuccessfull early Garand semiauto rifle, and AAI's post-war SPIW and ACR entries.
 
Mr. Popenker,
You are in fact correct.
I can't for the life of me figure how I associated the Degtyarev design with a primer actuation.
I like the locking flap design setup on the Degtyarev. Not much moving mass there, has the potential for a really high rate of fire.

Do you know where I might find a drawing of the AAI designs?

Sam
 
M14 used a gas cylinder/separate piston arrangement to drive the op rod, which correlates to a long and complexly-shaped bolt carrier, sorta. The stroke is longer than the M1 Carbine's short-stroke piston, but shorter than the attached-piston jobs like the AK and FN systems described above as "medium-stroke". Seems those two drive the piston the full length of the operating cycle, just like the M1, but reduce weight by moving the gas port back from the muzzle.

I find the beauty of the M14 system is that it includes a cut-off function that tends to correct for low-pressure rounds quite nicely, to far lower ammo levels than the vaunted (need i say over-rated?) FN manual adjustment system. The cut-off seems to be designed to allow the system to approach the praised "over-powering" of the AK gas system with bullets up to 175 grains (within some powder and hot-rodding limits), while giving the equivalent of extreme adjustment for low-powered ammo, without any need to stop the action and mess with the rifle.

I've heard that the M60 GPMG uses a gas piston similar to the M14, but it's been too long since I've been around one to remember clearly.
 
Jim, could you clarify the difference between "short" and "medium" stroke as in your post? I have never heard of that distinction, just long (more or less has to be attached to bolt carrier) and short (not, so just moves as far as needed).

I had also been under the impression that short (mid?) systems tap, while long systems push.

Anyone seen the piston on the Japanese .223 (type 89?). Its what I used to call short-stroke, but in two pieces, specifically to stagger and buffer the impact of the piston on the carrier. Based on some other japanese products I have intimate knowldege of, this seems very right to coddle and assume fragility on everything, even a rifle.
 
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