Could someone explain 'delayed blowback'?

P

pocat

New member
OK - I feel like a total idiot asking this question, but how exactly does the recoil action "work" on a semi-auto pistol such as 1911's, Glocks, etc.?

I believe this is called "delayed blowback", where the barrel drops down before the slide cycles back when the gun is fired. I fully understand the "gas action" system in rifles such as AK's and AR's, where the pressure in the barrel is re-directed back into the action causing the bolt to unlock and cycle another round, etc.

I have owned several semi pistols, and have disassembled every one, but I don't really understand the physics involved in this. I can't seem to grasp how or why the breach area (is that the right term?) has to lock into the slide, and then unlock and tilt in order to operate. What is the purpose of this? Also, some of the infamous "junk" guns like Jennings, Bryco, Lorcin, etc. have "fixed" barrels and operate on what I think is called "direct blowback."

I read once that on good semi's, the breach area and the barrel bushing in the front of the gun has to be tight and consistent in battery in order for the gun to be accurate, which I understand, but why aren't the "junk" guns more accurate since they have fixed barrels that maintain the same position? I also think that when a powerful cartridge is used, direct blowback is not feasible because the recoil spring would be so strong that you couldn't pull the slide back. I just don't understand how delayed blowback absorbs recoil just by the barrel tipping upward. (Note: I'm in no way implying that the "junk" guns are superior - I believe that the fixed barrel is one feature that makes them junk. But why?)

From my lack of understanding, I'm assuming that John Browning over-engineered the semi-auto, and most gun manufacturers since then have followed suit. Say it ain't so!
 
<snip>John Browning over-engineered the semi-auto, and most gun manufacturers since then have followed suit. Say it ain't so!
Click to expand...

Ain't so! I'll let someone else better at 'splianing the technical side do that. I understand how it works, but can't put it into print. (holding the 1911 Colt up to the monitor and showing you won't do much good either ;))This might help:

www.m1911.org/1911desc.htm

As to the "junk" guns being inaccurate. It's mostly in the loose fit and quick workmanship. Some of the cheap blowbacks have outstanding accuracy. (Some of the most accurate guns made use a fixed barrel and straight blowback action Ruger MarkII, High Standard and S&* Model41 come to mind as well as the Walther PPK.) They(the cheapies) just break easy and often, as well as having a lot of jams. Also, the higher pressure/recoil rounds like the 9mm Luger, .45acp and .40S&W would require an excessivly heavy recoil spring. If you get a chace to compare a Browning Hi Power in 9mm to one in .40S&W you can see pretty quick what I mean.
 
I would add that the substantial friction of the bullet being jammed through the barrel, helps hold the barrel forward until the bullet exits.
 
Aircarver,

Now that was funny. You need to go back to physics class.

A recoil operated firearm, as are most semi-auto handguns, depends on the energy acting in the opposite direction to actuate the mechanism.
For a locked breach gun the barrel and slide stay together for a short distance until the bullet has exited the bore and the pressure has dropped before unlocking. This is usually determined by the camming surfaces plus the spring strength and slide mass.
For blowback handguns the weight (mass) and strength of the recoil spring are the only thing normally keeping the slide in place until the bullet has exited the barrel. In some guns the chamber has flutes to further retard the opening process.
There is a neat design developed recently in europe where they have tiny holes drilled in the barrel in front of the chamber and the gas from these holes impinge against the shoulder of the slide at the front of the ejection port and this retards the opening.
There are many calculations which go into figuring all these things out so that the gun works with most ammo.
 
Locked breech guns are too powerful to hold closed with a mass of acceptable carry weight. The barrel forward force provides the additional force necessary to hold the barrel & slide locked together until the bullet exits.
 
I would add that the substantial friction of the bullet being jammed through the barrel, helps hold the barrel forward until the bullet exits.
Click to expand...

This would only work if the bullet were launched from outside the barrel, a la a revolver, no?

A couple of definitions:

"Blowback": An operating system consisting of a fixed barrel and a moveable slide, the latter of which is operated by the thrust of the case head. Locking of the breech until the projectile leaves the muzzle is performed solely by the mass of the slide.

"Short Recoil Operated": An operating system where the barrel is free to move along with the slide for a distance of less than the overall length of the cartridge (as opposed to "long recoil"), the barrel helping add to the mass of the slide and remaining locked together with it until the bullet has left the muzzle.

"Delayed Blowback": A system in which the conventional fixed barrel/moveable slide blowback operation is aided or "delayed" by some manner of mechanical disadvantage the slide must overcome in order to move to the rear. Often accomplished with roller cams or gas ports. This enables the simple blowback system to be used with more powerful cartridges without requiring inordinately stiff recoil springs or overly massive slides.
 
So - from what I'm gathering so far, the barrel and slide stay locked together until the bullet has left the muzzle, and then the unlock, barrel tilt and slide recoil takes place. Is that it? It would be very interesting to see a gun fired on a high-speed camera that would show this whole process in very slow motion.

I know that several (if not all) .22 semi's have fixed barrels, and they are very accurate. My Ruger 22/45 is. I'm confining my question to the centerfire 1911/Glock - type actions...
 
"This would only work if the bullet were launched from outside the barrel, a la a
revolver, no?"

In a pistol, from ignition, the bullet is driven into the rifling and during deformation and static friction imparts a maximum force forward on the barrel. The lugs holding the barrel & slide together use this force to retard the slide. (which is already trying to go back) As the bullet accelerates through the barrel it translates to sliding friction (which is less) and the 'forward force' on the barrel lessens until the bullet exits, when it goes to zero. the slide is moving slightly at this point and drags the barrel back until it unlocks, and continues it's stroke until the impulse imparted on the breechface is dragged down by the recoil spring.

This effect works on a revolver too, but probably acts only as a small retarding force on muzzle flip.
 
pocat,

The system you described in your original post is "Short Recoil", not "Delayed Blowback". Delayed blowback is used only on the HK P7 and P9, the Heritage Stealth, and the Vektor CP-1, AFAIK. (Roller-delayed on the P9, gas-delayed on the rest.)
 
All I can say is that aircarver is right. Until bullet leaves the system
of "slide and barrel locked together", this systen may be considered "a closed loop", containing some kind of a "gas spring"
holding the lock in tension and preventing unlocking. When bullets leaves the barrel, only then recoil action pushes slide/barrel system backwards and unlocking actually takes place...

Of course, this applies to breech lock pistols, not blowbacks.
 
Delayed blowback if memory serves me right has no locking system whatsoever, but uses some form of delaying device or mechanical leverage to do it's work (if memory serves me right it wolud take a 27lb. breech block to make the weapon safe/tolerable to shoot in a 30-06 size ctg. with a straight blowback action), only after most of the pressure has sudsided (albeit the bullet might still be in the barrel as the breechblock starts it's rearward travel), and for the most part is only used in high pressure cartridges (rifles and machine guns).
 
Here's some more info for all y'all:

A previous discussion right here on TFL:
http://thefiringline.com/forums/showthread.php?threadid=58494

Neat little animations here:
http://www.m1911.org/1911desc.htm

I haven't read this one yet, but it looks OK at first glance:
http://www.rkba.org/guns/principles/operating-systems/index.shtml

It would be very interesting to see a gun fired on a high-speed camera that would show this whole process in very slow motion.
Click to expand...
Ask and ye shall receive.

(video using some kind of super-nifty high-speed camera system from Germany, poke around this site for a bit, too. (these are VERY cool!))
http://www.kurzzeit.com/index_e.htm
 
Speaking of the Glock and the 1911, why is it that seemingly all modern auto pistols use a cam operated tilting barrel and not the link type of the 1911? As I understand it, JMB designed the cam operated system as well for use in the Hi Power. So what are the advantages of the cam system over the link system? Thanks.
 
I started out with a Norinco 1911, then a Colt, then two Kimbers.

Kept the Colt because I got too much into it to ever break even and besides, it is an all time classic pistol.

I have an H&K Compact .45 and a few other cam operated barrels.

My guess would be that the cam does exactly what the link does, that is it provides for a controlled release of the barrel from battery with the slide. But the cam eliminates at least two parts, the link and the link pin.

A manufacturer may be able to get a more precise release using a cam because of the ability to determine the exact release curve, as opposed to only having an arc to work with. This is purely my speculation only but it is based on looking at the cam profiles too.

Fewer parts means cheaper production and less to break. You can get the 1911 links in different lengths (center to center) if you are good enough to know how to measure and then determine the proper length required. There is the standard length and then a few longer and shorter links depending on your needs. That is advanced smithing and beyond my limited abilities.
 
Gentlemen,
Lets not forget the
Beretta 92 is a "delayed "recoil
type gun. It's barrell does NOT
tip (goes back & forth in line )
but drops a ( Walther Type ) block
after a short recoil,to halt the
barrell, and allow the slide to
complete its cycle .
Ponty
 
I may have mispoke on the
Beretta 92 . Some may say it's
a "short recoil" type because the
barrell and slide are locked together for a short distance .
Until the block drops.

Ponty
 
GRD, cool german site :cool: !!
The Beretta 92 is a "short recoil" gun, just like the brownings, only the lock used is different, a la walther.
The cam not only is simpler and stronger than the link and pin, but also more flexible, since you can regulate the point at which the barrel drops. This is not possible with the abrupt opening of the link. In any case, this advantage is mostly theoretical, since it is easy to "time" a 1911.
A "blowback" pistol can handle a fairly powerful cartridge without being too heavy, see the Astra 600 and more recently the HK VP70, both in 9x19. The thing is, in a blowback weapon the case is already being extracted (or, more correctly, pushing backwards) in the moment of firing, while the bullet is in the barrel and pressure is high, and you have to deal with the friction of the case walls against the chamber, if it grips too much the case can break in the base. The "short recoil" system is much more forgiving at the expense of a little more complexity.
A little tidbit: in a blowback gun if you block the barrel you'll have a much stronger (possibly dangerous) push rearwards, with very high slide velocity. In a short recoil pistol if you don't allow the bullet to move forward then nothing will move (if pressure is contained), the slide and barrel need the bullet to move forward in order to recoil backwards and unlock.
 
Teuf is correct.

Delayed blowback means that the slide and barrel are not physically locked at the moment of firing as they are in a 1911 or a Sig.

Delayed blowback simply means that there are mechanical devices on the gun that work to prevent the slide from immediately going out of battery when the round fires.

The two common examples of delayed blowback are the HK P7 series, which uses a gas tap and piston arrangement to keep the slide closed until chamber pressure drops, and the CZ-52, which uses a roller arrangement to delay slide opening.
 
Hi, guys,

The Browning designed tilting barrel is not the only way to achieve a locked breech. The Beretta 92, Walther P.38, Japanese Nambu, Luger, Mauser C96, etc. all are short recoil operated, locked breech pistols, yet the barrels do not tilt to unlock.

Note I said "recoil operated". The statement that the barrel and slide (breechblock) are held together by the forward force of the bullet on the barrel is not correct. The forward movement of the bullet causes an equal reaction backward of the barrel and breechblock as a unit. When the mechanism allows unlocking, the inertia of the breechblock keeps it in motion to extract and eject the empty case and pick up a new round from the magazine before the momentum of the breechblock is dissipated and the recoil spring reasserts itself to bring the breechblock back to pick up the barrel and return to battery.

Again, note RECOIL operated. IF THE BULLET DOES NOT MOVE, THE GUN DOES NOT OPERATE. If the barrel in, say, a Model 1911, is blocked so the bullet cannot move, neither the barrel nor the slide will move. The same is true of other recoil operated pistols.

These guns are not "delayed blowback" or "retarded blowback". They are true locked breech pistols. Until the unlocking takes place, they are just as locked as, say, a bolt action rifle.

Jim
 
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