DELAYED BLOWBACK DESIGN

[OLDSTER]

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.

 

[Faulkner]

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.

 

[Steve912]

Is the question mechanical, or philosophical?

There seems to be a few...

List of delayed-blowback firearms - Wikipedia

 

[pharmer]

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

 

[Kurusu]

I have two of the type.

Savage 1907

CZ vz. 24

 

[PALADIN85020]

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

 

[Onomea]

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?

 

[Steve912]

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.

 

[Onomea]

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?

 

[Absalom]

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?”

 

[OLDSTER]

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?

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.

 

[Onomea]

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?”

So all blowback pistols are delayed blowback?

 

[PALADIN85020]

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

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

 

[Absalom]

So all blowback pistols are delayed blowback?

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.

 

[Onomea]

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

 

[LVSteve]

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.

 

[Absalom]

The 1911 and the Glock use the Browning form of delayed blowback.
......
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.

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.

 

[PALADIN85020]

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

 

[2152hq]

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.

 

[PALADIN85020]

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.

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