Straight and Delayed Blowback: Five PCC Operating Systems

Roller delayed blowback and radial delayed blowback are 2 kinds of PCC operation system
January 28, 2021
Categories:Arms and Armor

The pistol caliber carbine, or PCC, has become a prevalent weapon’s platform as of late. Why not? Pistol ammo is cheaper, easy to find, and AR 15s have gotten boring for many of us. PCCs also come in a wide variety of designs, and today we are going to look at such PCC operating systems as the delayed blowback (radial and roller), straight blowback, and others. We’ll explain how they tick and maybe even how they tock. 

1. Straight Blowback – The Basic PCC Setup

Straight blowback is the most simplistic operating system available for PCCs. Like most things PCC, straight blowback came out of the world of SMGs. Straight blowback systems work simply. The bolt rests against the chamber of the barrel and is not locked in place. You pull the trigger, the round ignites, and the force pushes the projectile forward and generates a rearward force that propels the bolt to the rear. 

The CZ scorpion has a straight blowback

The CZ scorpion has a straight blowback system.

The movement has to be slowed or delayed in some way. The delay must be long enough to ensure the bullet leaves the barrel before the case leaves the chamber. A straight blowback gun uses a massive bolt, a heavy spring, or some combination of the two to create this delay. Most PCC AR 15 kits are blowback designs. 

Straight Blowback Examples—CZ Scorpion, KelTec Sub 2000, Hi-Point carbines

Pros

Simple and Cheap
Reliable

Cons

Heavy bolts can increase weight, and heavy springs can challenge ergonomics.
Heavier recoil

2. Radial Delayed Blowback 

Radial delayed blowback is a system created by CMMG for their famed Banshee series. The Banshee series encompasses numerous PCC calibers and is useful for 10mm, 5.7×28, 9mm, and more. The system works by combining a proprietary bolt and chamber designed for AR 15 upper receivers. 

Banshee Mk17 - Blowback action

The Banshee Mk17 – Blowback action utilizes the recoil of a round fired to operate the bolt, but there must be a means to delay the recoil, via bolt mass, radial delay, roller delay, etc.

The bolt looks and functions like a AR 15 bolt, except the lugs on the bolt, are cut to be angled, and this allows them to rotate and lock into the chamber. When the weapon is fired, the bolt has to rotate to unlock, and this creates the necessary delay to allow the bullet to leave the barrel before the case leaves the chamber. This system eliminates the need for a heavy bolt or spring and allows the gun to be nice and lightweight. 

Radial Delayed Blowback Example – MK17 Banshee

Pros

Reliable
Eliminates heavy bolt and springs

Cons

Only available in AR platforms.

3. Roller Delayed Blowback 

Roller delayed blowback firearms are an old school design, but a very effective one. The most famous rolled delayed SMG or PCC is the MP5 series. Roller delayed firearms utilize rollers built into the bolt that locks into designated ports in the gun.

Die Hard John McClane MP5 delayed blowback firearm

John McClane’s MP5 is an example of a roller delayed blowback firearm. Blowback firearms have an unlocked breech and recoil operated have a locked-breech design.

 When the weapon is fired, and pressure wants to send the bolt rearward, thive rollers prevent that. Roller delayed blowback creates a friction delay that keeps the bolt closed until the bullet has cleared the barrel. The roller delayed system works well with stamped guns.

Roller Delayed Blowback Examples – MP5, Garrow Arms Uppers

Pros

Eliminates heavy bolts and springs
Reliable
Works with stamped guns

Cons

Expensive and complicated design.

4. Dead Blow Action 

Dead Blow Action is a modified variant of a standard blowback action designed by Ruger for the Ruger PCC series of rifles and pistols. 

Ruger PCC dead blow action

The Dead Blow Action utilizes nothing more than an added tungsten weight to the bolt. When combined with a blowback-operated system, it creates an effect similar to a dead blow hammer.

The tungsten bolt can move forward and rearward, and as the bolt travels to the rear and slows, the tungsten weight slams forward, forcing the bolt to travel forwards. The end effect is the bolt travels less than a standard blowback action. 

Dead Blow Action Examples – Ruger PCC and PC Charger series

Pros

Inexpensive
Generates less recoil

Cons

It still requires a heavy bolt.

5. Short Stroke Gas System 

Short stroke gas systems are popular on modern rifles in rifle calibers. PCC rifles and pistols using short-stroke gas systems are very rare. Short stroke gas systems utilize a piston system that is attached to the barrel and a gas block. As a round is fired, gas is generated from the cartridge fired, and some are siphoned off through the gas block. 

Sig Sauer MPX

Sig Sauer MPX.

This gas propels a piston that is driven rearwards and strikes the bolt. The bolt is sent rearward and continuing the cycle of operations.

Short Stroke Gas System Examples – SIG MPX

Pros

Lightweight
Reliable
Proven

Cons

Expensive for PCCs 

The PCC World

The World of PCCs and submachine guns are rather large and full of all sorts of different fun guns. While almost all use some form of blowback action, the difference in how they handle is significant. The price difference is also no laughing matter. These are fascinating firearms and the different way engineers have recreated the mousetrap could fill a book. Or well, at least an article on it.

 

 

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