A couple gun buddies and I are debating the validity of the so-called "delayed blowback" concept. I can find no empirical, scientific, mathematical, or engineering records to prove the actual existence of the design and/or performance data to prove or disprove the validity of this theory. Can anyone share some knowledge on this debate; not theory, but actual proven data.

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John

I have heard the Colt Model 1903/1908 pocket pistols referred to as delayed blowback.

I believe the first generation Ruger PC4 & PC9 rifles are also referred to as delayed blowback.

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- Change it back -

Is the question mechanical, or philosophical?

There seems to be a few...

List of delayed-blowback firearms - Wikipedia

I have an HK 91, firing pin housing cams the rollers into their grooves just long enough for the bullet to clear the barrel. To me, pure genius if a little heavy. Joe

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Behavior Creates Destiny

I have two of the type.

Savage 1907



CZ vz. 24

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Expect the unexpected

This John Pedersen-designed pistol had a unique hesitation lock, essentially making it a delayed blowback. It was a bit complex (typical with Pedersen), but it worked quite well. This was probably one of the most ergonomic pistols ever made.

John

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- Cogito, ergo armatus sum -

What is the concept? Never heard of it.

Is the idea to deliberately engineer a pistol so that the blowback is delayed and thereby recoil is reduced?

To delay breech opening, until bullet exits muzzle and
residual pressure in barrel drips to "safe" level.

Do some people think non delayed breech opening blowback pistols are unsafe?

I’m a bit puzzled by this discussion. Maybe I should get my first cup of coffee. Is this meant to be facetious? It’s somewhat like “Do owls exist?”

That is my side of the "friendly" argument. Reduce felt recoil and save wear and tear in the pistol by slowing down slide velocity. ?? The example I use in my side of the debate is; The Makarov pistol is not touted as a "delayed blowback" design, and felt recoil is nasty.

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John

So all blowback pistols are delayed blowback?

No. In centerfire pistols that operate as simple blowbacks, the recoil spring (and sometimes the hammer mainspring) must be fairly stiff to prevent the breech opening while gas pressure is still high and the bullet has not left the barrel. Delayed blowback pistol slides can be retracted with less effort, as stiff springs can be moderated. Also, the recoil impulse is spread over a longer time period, in effect reducing felt recoil.

John

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- Cogito, ergo armatus sum -

No. The difference is between locked-breech (barrel and slide move back together a bit before unlocking to allow the pressure to dissipate) and blowback (barrel is fixed, slide blows back). Now delayed blowback means the barrel is still fixed, there is no locked breech, but the slide’s or breechblock’s/bolt’s blowback is delayed by a mechanism to dissipate. As already mentioned, HK’s roller type is probably the most famous.

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Hmmpf! Thanks for the education, all. As a revolver guy, at this point I'm off to research owls...

The 1911 and the Glock use the Browning form of delayed blowback.
The Strike One uses the Bergmann system with a sliding locking block.
The Walther P38 and its Beretta progeny use a swiveling locking block.
The Grand Power, Beretta Cougar and other weapons use a rotating barrel as part of the locking/blowback delay system.
The Luger uses a weird thing called a toggle lock. It seems to work, but I've never quite got my head around it.
Then there is the roller delay system, another mechanical dark art.


All the above are considered locked breech systems where the slide and barrel are mechanically locked together for a period, hopefully long enough to allow the pressures to reduce to a sensible level.

Then there are gas delayed blowback systems that use pressure form the fired round to delay or drastically slow down the opening of the action.

The HK P7 and the Walther "Soft-Coil" guns use a chamber with a piston attached to the slide.
The Steyr GB uses a chamber formed by the slide and a structure on the barrel.

Hope this helps.

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Release the Kraken

And that’s where it gets murky in terms of definition. It is indeed common to do as you did and wrap anything that’s not a pure inertia-plus-spring mechanism under delayed blowback.

But that gets a bit unfocused.

I prefer limiting the term to those systems that specifically do nothing but delay the blowback, and not include those that accomplish power management by additional means like locking the breech and redirecting the force vectors.

And just for some gun porn, here’s where I first learned about delayed blowback in the 1970s: the HK P9S.

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Unlocked or non-hesitation locked higher-power pistols are rare, but these do also exist. This H&K VP70 Z pistol was the first polymer-framed pistol, in 9mm Luger chambering. It was pure blowback. It relied upon the heavy slide and a stiff recoil spring to retard the slide when fired. However, because of its polymer frame, it weighed almost the same as a military 1911. It came on the market in 1970; this example was shipped in 1981.

John

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- Cogito, ergo armatus sum -

The Astra 600 in 9mmLuger as well as the earlier Mod 400 in 9mmLargo were both straight blowback actions.
The very heavy springs and O/A heavy weight do the job.

The Spanish Campo Giro semi Auto pistol (1912/1913) was a delayed blowback design. Chambered for the 9mmLargo.
A Spanish Service pistol.

The orig TSMG though not a handgun used a bronze block engaging the steel breech bolt at a slight angle. The two dis-similar materials thought to slow down the action speed as they slipped apart.,,at least slower than if the block had been made of steel like the bolt.
The idea was to create a delayed blowback action in the weapon.

Some say it's nonsense science (that principle itself).
Whatever,,the later WW2 versions of the TSMG , the M1 (M1A) were made straight blowback and w/o the complicated system. They seemed to work OK.

I have one those Astra 600/43s, made for the Germans during WWII. The really stiff recoil spring made the slide almost impossible to retract, and the recoil was brutal when fired. It worked but its ergonomics were horrible.

John

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- Cogito, ergo armatus sum -

Ah yes, the dubious "Blish Device".

I was hoping someone would bring it up.

Thanks!

John

Thanks guys for all the input. Now when our friendly debate reconvenes, I'll have more educated info. to support my side.

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John

One of the recent NRA magazines did a review or something and explained delayed blowback and undelayed(?) blowback. Can't remember a darned thing except the delayed was easier to shoot.

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Waiting For The Sun.

I believe that my AMT Automag II in .22 WMR can be considered a delayed blowback design. There are a series of tiny holes around the circumference of the chamber about halfway down. They lead into another chamber formed by a sleeve that is around the outside of the firing chamber. The idea being the brass case expands upon firing and into the holes a little bit and when pressure drops the case contracts, the grip on the chamber lessens, and the slide gets blown back to extract & eject and feed the next round.

I suppose the outer chamber around the firing chamber is to contain any gas should the case rupture and leak through the holes. You can see a series of blackened dots or dimples around the fired case corresponding to the holes in the chamber.

H&K G3. Battle proven around the world...

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Jorge

I've had 2 delayed blowback pistols, both based on the Pedersen system.
PMR-30 22 WMR
R-51 9 mm +P rated
Both function reliably. The 9 mm is interesting to compare to the plethora of tilting barrel pistols.
You get a lower bore axis hence more compact pistol.
You get a slide that's easy to rack for a subcompact.

OTOH, is the extra complexity in the mechanism worth it? Probably not.

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To cannon, all men are equal

Delayed blowback, aka retarded blowback, is a fine design used on some of my favorite pistols. They're typically very accurate because of the fixed barrels. The downside is the internals accumulate fouling quickly and require frequent cleaning. It's a much more complex design than a gun with just a heavy slide and recoil spring.

The H&K P7's are one. They vent gasses into a chamber to slow the rearward movement of the slide, via a piston. It's basically the opposite of a gas operated semi-auto.

My other favorite is the Steyr GB. I've got three of them now; a standard model shooter, a NIB standard model and a military model. I also have two of their muzzle breaks, which are fairly scarce, reduce recoil even further and add to the "cool factor". These have internal ports and piston rings on the barrel, that vent gasses between the barrel, slide and frame to keep the action closed until pressures drop.

Please ignore the Browning GP Competition, the Kimber and the Glock...

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And then there is the most common delayed blow back pistol being sold today... don't forget the Hi-Point with it's beluga whale sized slide.

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Conrad
SWCA #1830 SWHF #222

Our very own S&W Model 1913 illustrates the problem with direct blowback, but in a different way:

It had not just a fixed barrel, but the entire top cover was one rigid unit. It had no slide, just a breechblock/bolt that cycled out the back of the gun.

The mass of that was so low that even the .35 Auto caliber (basically a .32 ACP) required a massively strong spring to contain the force.

So they came up with an ingenious solution: A cross-bolt that lets you disconnect the bolt from the spring and cycle it to chamber a round without any effort. This was possible because another unusual feature is that the spring is a pull-, not push action. It is located above the barrel and stretched as the recoil drives the bolt back and does its work upon contracting, the opposite of standard recoil springs.

(Not my photos, borrowed from the web)

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Have a look at the Walther CCP series, also with gas "delayed" mechanisms.

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Alan
SWCA LM 2023, SWHF 220

Started thinking about this and with the exception of my Styer GB, all of my delayed blow back firearms are HK

I am exceptionally fond of all of these

The roller delayed system that HK uses is truly amazing



The locking piece (orange) comes in about 6 different angles. These alter how long the bolt is delayed.

As an example other than firearm markings the difference between MP5s chambered for 40 S&W and MP5/s chambered in 10MM auto is the barrel and the locking piece. All other parts are interchangeable

MP5s chambered in 357 SIG or MP5/10s firing the watered down 10MM Auto ammunition use the same locking piece as the MP5/40

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"Acta non verba"

My understanding of the Blish Lock used in the Thompson SMG was to delay cycling. It was not needed for the gun to work and was removed from subsequent models, as mentioned above. However, it was noted that the cyclic rate increased when the Blish Lock was removed.

Currently CMMG makes a PCC using a rotary bolt. The bolt must turn to allow the bolt to cycle, forming something of a delayed blowback.

The Machine Gun Vol 4 has sections on both delayed blowback and retarded blowback. Along with other action types)

I have one and have to say, kind of like it. It's too bad the trigger pull is so heavy, but it does take the firing pin spring from full at rest to fully compressed. About as safe and fool proof as one can get. The trigger can be learned so that once the long take up is through a not so bad "single action" break is had.

Rifling on the VP70 contributes to manipulating the action. It's considerably deeper than conventional rifling, causes the bullet to slow (with a resulting decrease in fps) imparting longer and greater rearward pressure on the slide.

The Rock Island Armory’s XT22 also uses delayed blow back.

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Some of the 38special W/C Target pistols built on the 1911A1 Colt that were straight blowback actions used shallow rings cut into the walls of the chamber.
IIRC Colt used the system when they factory built their pistols on the Natl Match 1911 as did a few of the custom makers.

The idea was that the case upon expanding on firing would grip those rings/grooves in the chamber momentarily and hold the action closed (delayed). Then let go and allow the action to function as a regular blowback action.
The linked-locking bbl to slide system was done away with in the guns.

Some of the custom builders (Clarke?) used the orig linked bbl locking system of the pistol in their 38specl W/C Target conversions.

There is also the 9mm High Point but I will not post a picture,

to prevent any eye damage to any of you that only enjoy looking at "Pretty" weapons.




( high standard..changed to "Point" ) sorry

Hi Point is straight blowback. Granted the slide and recoil springs are heavy, but it’s straight blowback

Absolutely not

The Hi Point is not delayed blowback. Its simply blowback.

I'm not quite understanding the OP's question. They have been around over a century. Its not a difficult concept to understand.

I own quite a few delayed blowback pistols. All of mine are high end and very well made handguns. I'm a big fan of the delayed blowback.


Laugo Alien Pistol (gas delayed)








Korth PRS (roller delayed)








Benelli MP3S (lever delayed)








HK P9S (roller delayed)













HK P7 (gas delayed)























Korriphila HSP 701 (roller delayed)













AJ Ordnance Thomas (lever delayed)








Steyr GB (gas delayed)








MAB PA-15 Target (torque delayed)

Didnt see any mention of the CZ52 above,
(Maybe I missed it), btw no mention of it in the posted Wikepedia link either,

A few years back they were plentiful at gun shows, still recall seeing them lined up on dealer tables and thinking...Yick...that's one ugly handgun..... Yet , slowly they started to grow on me and for a C note with 2 mags, a military holster, cleaning rod and a couple of boxes of HOT combloc copper wash PPSH SMG Tokorov ammo how could you go wrong ?
When I got it home I figured out how to remove the slide so I could check it was clean and functioning... (very easy btw, CZ52s come apart kinda like a Mauser HSC or HK4 with a takedown lock in the front top trigger guard housing )... After getting apart and peering into its innards I went.. What the ?
suddenly realizing it incorporated a miniature roller locking system...
(Btw I am a fan of the MG42, CETME, G3 and P7)....this made me appreciate that gun even more.

They are still out there and not that expensive if you can get past its aesthetics...
Some sites recommend replacing the rollers and firing pins with aftermarket stuff so do your research.

Ps...recall seeing some 9mm conversion kits out there back then as well.

That’s because the CZ 52 is not a delayed blowback. It’s a roller locking system, not a roller delayed blowback.

Completely different

I understand it is a delayed roller locking system,
It's been a few years since it's been out of the safe, but while the CZ52 barrel is not fixed to the frame like HK P7 or Walther PPK, neither are the Mauser HSc or HK4 barrels which are simple blowback , always assumed the rollers locked the slide momentarily delaying until pressure dropped then unlocked allowing a delayed blowback.
Will have to do some research.
Btw the Wikepedia article did not include the CZ52 in with the roller locking guns either.

Not every blowback has the barrel fixed to the frame.

I think some folks are overthinking this. The easiest way to tell if a gun is a blowback, delayed or otherwise, is to rack the slide slowly and watch. If the barrel and slide remain locked together for a millimeter or two, you have a locked breech. If the slide pulls away from the barrel instantly, you have a blowback of some kind.

Try that with your P7 and then with your CZ and let me know your findings. The CZ 52 is in no way a blowback pistol of any sort. It’s a locked breech pistol. Not sure what delay you’re referring to except that the rollers lock the barrel to the slide, thereby delaying the separation. You can say that about all locked breech designs.

A delayed blowback requires the gun to be fired to lock and delay the cycle. A locked breech does not.

Found this World of guns cartoon cutaway slow mo of the CZ52 action,

While it does move linear to the rear
the barrel does move back with the slide while locked.
Still kinda neat, learn something new every day.

Ff to 2:00 mark if interested in seeing its function.
Slow Mo Of CZ 52 Pistol Firing (How It Works CZ 52 Semi-Automatic Pistol) - YouTube

Yes, its a locked breech. Many designs stay linear like that, such as a Walther P38 and Beretta 92 that use a falling block design. Not every design causes a barrel to drop or tilt.

Like I said, compare your CZ 52 and HK P7. One is a blowback, the other is not.

The mid 50's Kimball (sp?) semiauto pistol in 30M1Carbine caliber was a delayed blowback.
It used the grooved/ringed chamber concept to delay opening of the slide. The expanded cartridge case was to grip those rings in the chamber walls and hold on for a moment till the chamber pressure fell.

It failed. Probably for a number of reasons along with the delayed blowback system it used.
I know the slide would batter the simple recoil stop in the frame ( a pin) upon recoil. That put many out of commission quickly.

But 30Carbine ammo was cheap then and at least one idea was to market a semiauto pistol that would function with it.
This one didn't make the grade.

Yeah but wasn't that based on a Rheinmetall patent and used in the MG42?

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FFL08

Can one still say "retarded"

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Forum consigliere

Applied to things it probably scrapes by

The automated cockpit annunciator in the Airbus series counts down the altitude and then tells the pilots to retard (to pull back) the throttles just before touchdown.

I was showing this video of a A380 landing at SFO to my high school aviation class and actually had a girl ask "Why is it calling the pilot a retard?"

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