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ghostsniper1
Posts: 2,645 Senior Member
Somebody explain to me the blowback and gas driven systems.
ghostsniper1
Posts: 2,645 Senior Member
Im not a diehard in either designs or fields and I am just assuming that blowback SA's are cycled by the force of the spent cartridge against the bolt to "reset" it. And the gas driven is the pressure from the propellant charge sent rearward to drive the bolt back to reset it???? Is this correct in my thinking??? And if so, what is the difference? Which is better, worse, drawbacks???
Replies
"Nothing is safe from stupid." - Zee
Gas actions tend to be more complicated affairs, resulting in bulkier firearms but with a tendency to better function and reliability - to a point. These guns are sensitive to how clean they're kept, and to the pressures of the ammo being fired. In pistols, few gas-operated models exist, the Desert Eagle hand-cannon and the AR-based "pistols" are exceptions. The operation of the bolt is powered by the expanding gasses of the cartridge, most often channeled back to the bolt by a bleed-off port in the barrel leading into the gas tube, ordinarily (but not always) containing a piston and a rod that pushes the bolt back. These can handle higher pressures, especially as most designs incorporate a rotating breechblock that physically locks into the barrel to keep the action closed until the pressure in the barrel itself drops to a safe level for the bolt to open. Much more common in semi-auto rifles than in pistols.
A third pistol mechanism is the pivoting link, or tilting breech. Most pistols designed since the 1911 use some variation on this theme, where the barrel's breech cams up into position, held there by a combination of spring pressure and mechanical advantage until the gun is fired. Then, the recoil forces begin moving the works backwards, the barrel tilts down out of engagement (or rotates, as in the Beretta/Stoeger Cougar) in order to unlock, giving the necessary delay in breech opening until pressures are safe. This is the "default" system for major caliber pistol rounds such as 9mm, .40 S&W, .45 ACP, 10mm, .38 Super, etc. Browing High Power, Glock, and some 1911 versions use a linkless system, which makes the whole gun a bit easier to reassemble after field-stripping, the Beretta 92 uses a breech-locking system borrowed from the German Walther P-38 that gets a bit more complicated than the simple pivoting link of the 1911 but does the job. The advantage here is a more robust design, able to handle a wider variety of ammo pressures than the blowback, and quite a bit simpler and more compact than a true gas system.
There are other systems, and variations on the themes, but these basics will be quickly apparent with a little looking. The blowback Walther PP system, including the Makarov pistols, is an elegantly simple arrangement, the barrel is fixed to the frame and acts as the "guide rod" for the recoil spring that encircles it within the slide. This keeps the barrel pretty low over the line of your arm, helping control the muzzle flip of the pistol, which is harder to do with the mechanical link systems, as they generally have a separate spring guide rod beneath the pistol, as well as needing room under the barrel for the link, camming block, or whatever other feature is used.
Good question, hope this wordy description helps!
A blowback is the most primitive of self-loading designs. This type of mechanism uses only the mass of the slide and the tension of the recoil spring to hold the breech closed. It works well for cartridges of roughly .380ACP power levels and less. Anything bigger requires stupid-heavy slides and stupid-stiff springs.
A recoil-operated systems uses some form of mechanical lock to keep the breech closed until after the bullet has left the barrel. Think of it as a "speed bump" that allows the slide or bolt to travel rearward at a slower velocity than would be possible with a blowback. The Browning-designed tilting barrel on virtually all semi-auto duty pistols is the most obvious example seen today, but there is also the Browning 1917, 1919 and 1921/M2 machineguns, and the HKG3/MP5 series of rifles.
Gas mechanisms most commonly divert propellant gasses near the muzzle (of a rifle) against a piston which operates and unlocks the breech. Much like the recoil mechanism, the bullet is well out the barrel before this actually happens. The AR-15 and Swedish Ljungman (SP?) are a little different in that they eliminate the piston in favor of routing gas directly back into the bolt where it performs the same function. This system is typically dirtier than the piston type, but is lighter weight and has more accuracy potential due to lack of stuff moving against the barrel.
Hope that helps.
Then you have some real weird ones like the HK P7 pistol. As I recall, that thing uses gas pressure to delay opening of the breech
"Nothing is safe from stupid." - Zee
Great post, Thanks.
Snake
What's the recoil feel like compared to modern 9mms of similar weight? (38 oz.?????)
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
Hmmm , good question. Did have it out recently with some other WWII pistols like a P-38 , Luger , Radom and Hi-Power , and there's really no noticable difference. It's not as sharp as a PPK or my CZ-82.
How easy it is to make people believe a lie, and [how] hard it is to undo that work again! -- Mark Twain
Master of understatement there, are ya?:tooth:
Mike
N454casull
It's not just slide mass and spring tension for this form of mechanism. It also utilizes the ballooning effect of the brass case in the chamber when the powder burns to form a momentary friction resistance against the inside walls of the chamber. This is evident in some older European designs in which six or eight length-wise grooves a couple thousandths deep or so were cut in to the chamber to allow the case to balloon in to them and hang on for a second before the case contracted to its former size after the pressure came down.
For handguns, mostly it's heavy, cheaper models. But the Astra is pretty handsome, in my opinion. I don't know about my P 7 H&K, I suspect it's blowback because it's got a strong spring and a fixed barrel. I need to read the literature, I guess.
Gas operated are mostly rifles because the mechanism is more complicated and best suited for high-pressure rounds. They operate the bolt by bleeding gas off the barrel into a gas tube and a piston that operates the bolt.
Piston-driven AR's have a piston right near the manifold off the barrel. The gas acts on the piston, which acts on the carrier, which moves the bolt.
That's the latest :yesno: arguement. The gas tube on current ARs is tough to clean , most use the big pipe cleaners with some getting them stuck. They also get HOT on rapid or full-auto. The AK uses a piston driven system.
The superiority of the piston system (more reliable , less maintenance) is being touted to the DOD , mostly by companies who want big dollar contracts.
Daewoo had an AR/AK hybrid which was very good 25yrs ago , but nobody noticed , or cared back then.
Depends on who ya ask , like the guy selling the jumbo pipe cleaners!
Though gas tube fouling was a problem in the early days of Viet Nam I heard.
Oh I agree 100%. But I have seen enough ARs with pipe cleaners and , believe it or not , those red plastic spray tubes , stuck in them to know that people will do the dumbest things. It's often said more guns are worn out by cleaning than shooting.
I think recoil will differ in a negligible way. I've shot piston driven ARs next to gas impingement ARs and I don't really see a difference in recoil.
Heat is a factor, however. Piston driven rifles tend to run cooler over all compared to gas impingement systems because the hot barrel gas is not being jetted directly on to the bolt carrier area, nor down a 7" long gas tube. The gas block of a piston rifle will get hot as the dickens, but the piston and everything behind it arent as bad.
We used to get pipe cleaners to clean our tubes, but it wasn't something we did on a regular basis. The gunk blew down into the carrier.
The P7 IIRC has H&K's often-used "fluted chamber", putting it in JasonMPD's described category - perhaps a "pressure-delayed blowback"? Haven't had the opportunity to check out any P7 fired brass, but I suspect you'll see the imprints of the grooved/fluted chamber on each case.
The P7 was a master of engineering IMO, the simplistic design of a fixed-barrel blowback system, with the innovative "squeeze-cocker" finger lever. Handled one or two in the shop, and they were, like most H&K products, built like a German race car.
Here's what I know. I don't know a great deal about a pure blowback type action but it doesn't lock up. The recoil type is what a Browning Auto 5 shotgun was. I do know they usually have more felt recoil than a gas system, such as a Remington 1100.
Son that's somebody with nothing to do with his time but keep me in trouble with mom.