Blow-Back, Breech-Lock? Pistol Actions Questions!

N

Nightcrawler

New member
Okay, awhile back, I was pondering why the .380 cartridge is still popular in the US, given that it's only 2mm shorter than 9x19, yet 9x19 is much more potent.

Now, back in the old days, putting higher pressure cartridges like the Parabellum into tiny guns was probably difficult, but we have much improved metallurgy these days (hence itty bitty 9mms like the Khar and the Kel-Tec).

Then I read somewhere that .380 can be chambered in apparently ligher, simpler blowback pistols, whereas 9x19 requires breech-locked pistols, or something like that.

Somebody wanna fill me in?

Another Question: The Desert Eagle is gas operated. Does it have a gas tube, then? Is it direct gas, like the AR? It must be; unless I'm very mistaken, cramming a gas piston into a package that small would take some doing. Why does it have to be gas-operated? I mean, if they can have .45ACP reliably cycle a pistol without gas assistance, why can't .44 Magnum do it? (Of course, I have the same questions regarding .308 rifles compared to 9mm submachine guns, though the HK series is recoil-operated).
 
Then I read somewhere that .380 can be chambered in apparently ligher, simpler blowback pistols, whereas 9x19 requires breech-locked pistols, or something like that.
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I think you've hit on part of the issue, the .380 has about 1/2 the ME of 9mm, so a smaller gun isn't such a problem. The recoil impulse from 9mm is just too much to absorb in a plain blowback action as a rule, the spring would be so strong that you couldn't cycle the action. Of course, the folks that brought you the Astra 600 didn't know that, but it has a truck spring for a recoil spring! It's also a handgul to chamber a round in that beast. :) There are a couple of blowback pistols in larger calibers, even one in .45ACP, but for the most part, anything above .380 or 9x18 is locked breech. Of course, some popular pistols in .380 and even .32ACP are locked breech too, it really helps soak up the recoil. My Colt Mustang in .380 is a locked breech, as well as the Keltec P32 in .32ACP.
 
It's all quite confusing.

The 9mm P is a high-power, high-energy cartridge. Putting it in a blowback gun neccessitaes a very heavy slide, as the mass of the slide, and it's inertia, are all that hold the breech shut while the bullet is in the barrel. If you put the 9mm P in a blowback with a light slide, it would open too fast, and release high-pressure gasses into the gun and shooter's face. Not good.

With a locked breech, the barrel is physically locked to the slide for the time it takes for gas pressure to drop to a reasonable level. Recoil energy from accelerating the bullet is used to impart momentum to the locked-together assembly, which is used to unlock the assembly and eject the case, while stored energy from a spring is used to reload and relock it.

Blowbacks technically are gas operated, as the combustion gas pressure against the cartridge and the breech face is used to impart momentum to the slide, not the recoil energy of the bullet.

All of the modern mini-guns are locked-breech. Even the Kel-Tec .32 is a locked-breech auto. The locked operation allows the rest of the gun to be built lighter, as the high energy levels are directed down the barrel. In the case of locked breeches on the .32 Kel-Tec, and the Colt Govt. Model .380, it allows for a REALLY small gun to be built, as the frame doesn'y need to be stout or heavy enough to withstand the impact of a fast-moving slide, and with the lesser slide velocity, the felt recoil is minimal.

There are exceptions to the locked/blowback rules. One was the Detonics Pocket Nine, a gun well known for it's severe recoil. Another is the Astra 400/600 series, blowback guns which are beefy, heavy, and with hammer and recoil springs so stiff they make it difficult to rack the slide. Astras, however, are big enough to not have prohibitive recoil.

There are compromise systems available, just to add to the confusion. Gas-delayed blowbacks like the HK P7 and the Heritage Stealth, or the obscure Steyr GB, use gasses tapped from the barrel to keep the slide from moving until the pressure has dropped enough by providing pressure against a piston, or the inside face of the slide, in the case of the GB. Other than the piston, there's nothing locking thebarrel to the slide in these guns, and they can be chambered in high-energy rounds, as the higher the gas pressure, the harder the slide is held shut against the recoil impulse. An imbalance between the size of the gas port in the barrel, the surface area that the gasses work against, and the amount of pressure on the breechface allows the mechanism to function, as the breechface is set up as a bit bigger surface to work against.

Desert Eagles are are gas operated mostly because they have the space to build such a system in the HUGE platform the gun represents. They're set-up that way because the heavy magnum rounds have a great deal of energy to contend with, making recoil operation problematic, as there's just a bit much to deal with. There ARE recoil operated heavy mags, though. The LAR Grizzly is a scaled-up 1911, and the Automag IV's and V's are Browning-style linkless tilting barrel set-ups. Coonan .357's are another example.

Not having a schematic in front of me, I don't recall the exact nature of the D.E. gas system, but I THINK it's direct-impingement, like an FN-FAL.. Don't hold me to that, I could be wrong. The memory is spotty, and I don't own one. They DO have a gas tube running under the barrel, with a port near the muzzle. You must never run un-jacketed bullets in your D.E., because you can clog the gas port, and turn your gun into a single shot that can only be repaired by the factory.

Some .308 machine guns ARE recoil operated. The Maxim gun comes to mind. Sub-machine guns are typically blowback, as a sub-machine gun is big enough that a heavy slide (Or bolt.) is not a detriment to handling characteristics like it would be on a handgun. Early Thompson sub-machine guns had a locking system, (The Blish lock. It operates on the differing friction coefficeints of different metals under pressure.) later guns were simple blowbacks as the locking system proved uneccessary, and it was simpler (Read: cheaper and faster.)to make the guns without it.

I hope this helps. Did I miss anything?
 
The FAL has a gas piston. I doubt the Desert Eagle does. THat would explain why it needs to be kept cleaner than your average pistol, like an AR-15 compared to an AK.
 
Oh, sure, John. Just answer the darn question whilst I type up an ARTICLE!.
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I just figured you liked to type! :D


I do have to disagree with one tiny point you made.
All of the modern mini-guns are locked-breech. Even the Kel-Tec .32 is a locked-breech auto.
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Of the .32ACP mini's, only the Keltec is a locked breech, and the Colt .380's are the only locked breech .380's that I can think of off-hand. Most of the .380 and smaller guns are actually blowback design. Small point, but we strive to be 100% accurate. :)
 
The Mak 9x8 is supposedly the nastiest thing a blowback design can take...given old technology, this is true. Given new tech. its not true..but the Para is ALOT more recoil intensive than most want in a blowback designed gun. All previous points are most accurate...I had an Accutech BL9...total POS, but never the less it was smaller than my Kahr K40 and was a 9mm blowback s/auto.
When I could get it to work, it worked well...recoil wasnt bad, very similar to my K40. Hi Point and others have blowback designed 9mm and larger calibered guns. While I agree that the spring/slide weight are critical issues with a more powerful blowback gun...the little Accutech seems to throw the theory out the window. If it was a better made gun...better materials and workmanship...I think they have a winner on there hands. Its roughly the same size as an MK series Kahr.
The locked breech design has inherent benefits over the blowback design anyway...it takes the "snap" out of the recoil impulse/cycle. It slows recoil and softens the initial hit produced by the cycle. Thus is a better design. IMO only. While both designs have individual merit...the blowback has fewer working parts to break/dis/assemble/clean etc.....some feel the fixed barrel design is a little more accurate than the browning design.
I feel both have strengths...and are worth looking at. Its simply a matter of taste and timing....Shoot well....
 
[bold]
Is there any advantage to a blow-back design, and if not, why do they keep making them?[/bold]
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Because they're simpler and less expensive to make, and because they function just as well (or better) for the smaller calibers.
 
The Mak 9x8 is supposedly the nastiest thing a blowback design can take...given old technology, this is true.
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Hmm... "old" technology gave us the Astra 400 in 9mm Largo, and the Astra 600 in 9mm para, they're a bit more than 9x18! :D
Astra_400.jpg
 
John, that point you disagreed with wasn't a disagreement. I was unclear. I SHOULD have said "mini-nines" , not "mini-guns". I meant the new crop of full-power autos like the Kahrs. Blowbacks are still being made, but I wasn't referring to them. My goof.

Nice Astra pic. My 600 is a bear to cock, but it's accurate as all get-out, and a hoot to shoot. It's one of the best "visually-indexed" point shooters I've had experience with. (That's aiming the gun with your peripheral vision with eyes on the target, while shooting from the hip, more or less. One-handed, of course. Steep-grip guns lend themselves well to one-hand operation.)

Although I do find that after 200-ish rounds of full-power ammo, my hand becomes decidedly tired of soaking up those repeated slide impacts, and starts to ache. I wonder about the 400 in 9 x 23 Largo, which has a good 150 FPS on the 9 x 19. Seem like it would wear you out faster, but I don't own one, yet.
 
Nightcrawler, which HK rifles/subguns are you referring to when you say:

"Of course, I have the same questions regarding .308 rifles compared to 9mm submachine guns, though the HK series is recoil-operated. "

I can't think of any HK rifle or subgun which is recoil operated.

Most, if not all, HK rifles and subguns, until the G36, were based on the delayed blowback principle, i.e. the roller-locked bolt system HK is known for - not recoil operation.

Just curious what you were referencing.
 
I had thought that the HK rifles were roller locking recoil operated.

Anyone care to explain the difference between recoil and blowback operated? Neither use a gas tube, and both rely on Newtonian principles of for every action there is an equal and opposite reaction, yes?
 
. I wonder about the 400 in 9 x 23 Largo, which has a good 150 FPS on the 9 x 19. Seem like it would wear you out faster, but I don't own one, yet.
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It so happens that I have a 400 too, and for some reason, the 600 seems to have more recoil. I mentioned this somewhere, and another guy had the same impression...
 
Nightcrawler, here is how I understand it . . .

There are three "basic" methods of operation for small arms:

1. Gas operated
2. Recoil operated
3. Blowback operated

Gas operation is familiar - AR15, AK 47, FN FAL, G36, etc...

Recoil operation refers to a method of operation in which the barrel and breech block are locked together. Upon firing, the barrel and breach block remain locked together and move rearward together under the force of the bullet casing's rearward momentum. After a short distance, the barrel is stopped from moving rearward, the breech unlocks from the barrel, and the breech then continues rearward, extracting the empty case. The idea is to create a sufficient time delay in the opening of the breech to permit high pressure gases to dissipate. Recoil does this by keeping the breach and barrel locked together for a short distance.

[Most common modern large caliber handguns work on some short recoil mechanisms principle, e.g. 1911 and all similarly designed tilting barrel designs (Hi-Power, Glock, Sig, etc...), Beretta 92 and similar locking-wedge designs (Taurus, Walther P-38), toggle arm designs (Luger), rotating barrel (Mauser M2) and roller-locking (CZ 52 - which is not same as HK roller locking). In addition, many full size machine guns and field artillary cannons rely on this method of operation. The only rifle I know of that utilizes recoil is the new Russian AN 94 assault rifle (but don't ask me how that thing works).]

Simple blowback refers to a method of operation in which the barrel and breech block are never locked together. Thus, the barrel never moves and the rearward momentum of the bullet casing acts only to move and open the breech block. The only thing keeping a blowback pistol's breach closed is the breech blocks inertia (weight) and the recoil spring. Hence the heavy bolts on first generation subguns that used simple blowback, e.g. Sten, Grease gun, Ppsh, and the stiff springs on simple blowback pistols which can't utilize a heavy breech block. The necessary time delay to let gases dissipate is achieved not by locking the breech and barrel together, but only by the shear weight of the breech block and the strength of the recoil spring.

For really high powered rounds, like rifle ammunition, simple blowback can't be used because the breech would be blasted open while high pressure gases were still in the barrel, thus endangering the shooter. HK calculations I've seen show that in order to utilize simple blowback in a .308 rifle, the breach block would have to weigh on the order of 36 pounds to be safe and create the necessary delay in the breech opening.

This drawback, however, can be overcome by using a delayed-blowback method of operation. The basic idea is to get the breech block to behave as if it weighs 36 pounds, even though it is only a few ounces. This can be done in a number of ways - friction (i.e. the above mentioned Blish principle in the Thompson) or gas delay (above mention HK P7 pistol) or mechanical delay.

Mechanical delay has been the most successful method. The two designs that come to mind are the HK roller-locked series of weapons and the French FAMAS. The basic idea is to use a 2 piece breech block (bolt) consisting of a breech face and a heavier locking piece connected to the breech face by a leverage system. The bullet casing pushes against the breech face, which is in turn connected vie a lever to the heavier locking piece. The force acting on the breech face is transmitted to and must first move the locking piece via the connecting lever before the breech face can open. The mechanical disadvantage created by the lever acting on the heavier locking piece makes the two piece bolt behave like a much heavier bolt, thus delaying the opening of the breech. Again, however, the breech and barrel are never locked together and the barrel never moves. The only thing keeping the breech closed is the weight of the bolt and the recoil spring strength - but, because of the 2 piece design and lever system, the weight and spring strength are amplified.

Hope this helps, and if anyone sees any mistakes in the above, please chime in.
 
A blowback pistol has some distinct advantages:

1. Simplicity = Reliability
2. Fixed Barrel = Accuracy

Buy a Makarov if you want a really well executed blowback design.
 
Neither is more less accurate than the other.

I once thought a fixed barrel design gun would be inherently more accurate than a locked breech/floating barrel design. But its not true...cant be. The barrel doesnt move at all...but the sights are fixed to a slide that still moves independently of the barrel.
The same is true for locked breech guns. Accuracy of course depends on the ammo, barrel quality and length...etc.

But the factor which exists with any gun design regarding accuracy is, how well sights line up with the barrel and how tight the lock down between the two are at the point of firing. Neither gun design has an advantage over the other in accuracy once that point is brought up. I just thought I would throw this in.....

No flame intended...as I once thought the same thing and was taught a different way of understanding.....Shoot well
 
Nooo. HK's are delayed-blowback, not recoil operated. Follow along.

The term "recoil operated' developed fairly early to describe the operation of guns like the Maxim, in which the barrel and breech(bolt) were locked together and moved rearward together for a certain distance before the barrel stopped and the breech opened to eject the spent casing. Again, the goal is to keep the breech closed long enough to let the high pressure gasses dissipate. Creating this time delay by keeping the breech and barrel locked together and letting them "recoil" together was one way of accomplishing this - and was termed "recoil operation." There are two flavors - short and long.

In HK's, the necessary time delay to let gases dissipate before the bolt opens is not created by letting the barrel and breech travel backward together for a short time/distance. Instead, the time delay is created by delaying the movement of the bolt (breech) alone. This is done by way of a mechanical delay system in which the bolt face must move a larger bolt carrier before the breech face can move rearward. The only thing that moves in HK's is the two piece bolt (breech), not the barrel. And the necessary delay is created only by delaying/slowing the rearward movement of the bolt.

Recoil operation is a specific term with a specific meaning - namely, operation in which the bolt and barrel recoil together to delay the opening of the breech. To apply this terminology to an HK roller-locked rifle is just wrong.

Similarly, to say that both HK's and guns like the Maxim operate on "recoil" simply because they both rely on the force acting backward against the spent shell casing is misleading and an oversimplification that doesn't account for the actual differences in what happens in those weapons. This is like saying that all automatic/semi-automatic firearms are "gas operated" because they depend on the rapidly expanding gases from the cartridge to operate their extraction, ejection, feeding, firing cycles. Again, that would be incorrect because the term "gas operated" has a very specific meaning and refers only to weapons like the AR or AK which tap gas from the barrel at some point and redirect it back to a piston/bolt/bolt carrier or whatever to operated and cycle the weapon.

Now, granted, the conceptual difference between delayed-blowback and recoil operation may be a fine line, but it is a very real line. They may both depend on the force exerted against a spent casing upon firing, but that does not mean they are both "recoil" operated. And the difference plays a big part in the design and operation of the weapons in question.

Now, if you want to continue calling HK's recoil operated weapons, then be my guest. It makes no difference to me. But unless you have an answer for why I am wrong, then at least stop rolling your eyes.

If you still need more education, then check out the following:

www.tpub.com/maa/85.htm
www.tpub.com/gunners/54.htm
www.rkba.org/guns/principles/operating-systems/delayed-inertia.html
 
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