Practically all shooters have experienced blowback. Not the type where something you did or didn’t do caused things to go sideways and have unintended consequences. No, I’m talking about the blowback operating system in rifle or pistol.
You’ve fired a semi-automatic .22LR rifle or pistol, right? Well, nearly every one ever built uses a blowback system because it is simple, economical to manufacture, and needs little maintenance. Most large-format pistols and rifles chambered in 9mm also use a blowback operating mechanism. The power from a 9mm cartridge is more powerful than a .22 rimfire, so the mechanism needs to be more robust.
In a blowback operating system, the expanding gases and recoil of the fired cartridge push the bolt backward to extract the spent case, with the action held closed long enough for chamber pressure to drop to safe levels through a combination of bolt mass and spring pressure. Once the action has fully opened and the extracted case is ejected, the recoil spring then pushes the bolt forward to load the next round. It’s a very simple concept.
The bolt mass and recoil spring are engineered to handle the specific recoil of the chambering of the firearm. Neither the bolt nor the recoil spring is too heavy, or too light. Too heavy, and the firearm won’t function. Too light and the bolt will batter the receiver into a pulp and transmit enough recoil to the shooter to rattle the fillings in your teeth loose.
As you have probably guessed, not all blowback firearms are built the same. There are two primary types: Roller-delayed blowback action and direct blowback action. Both accomplish the same thing, but in different ways.
A good example of a direct-blowback system firearm is the Springfield Armory SAINT Victor 9mm Carbine. This AR-style 9mm features a dedicated lower and upper designed specifically for the 9mm round, and feeds from 32-round, Colt-pattern magazines. Read more about this firearm in Will Dabbs’ SAINT Victor 9mm pistol review.
A good example of a roller-delayed system is the Springfield Armory Kuna 9mm. The Kuna’s roller-delayed system employs a roller to temporarily lock the bolt into battery, eliminating the need for a heavy bolt or gas system. It feeds from 30-round translucent polymer magazines. You can read more about this gun in Jeremy Tremp’s Springfield Kuna review.
What Are the Differences?
A direct blowback system is the simpler of the two designs. With a direct blowback system, the bolt relies on a combination of mass and recoil spring resistance. When a cartridge is fired, the case pushes back against the bolt face. The bolt provides resistance to the fired round’s force and slides inside the receiver as the recoil spring provides force and compresses under the force of the fired round. The rearward force is enough to allow the empty case to be ejected and to cock the hammer. Then, the recoil spring pushes the bolt forward, stripping a cartridge out of the magazine and loading it into the chamber. The firearm is then ready to fire.
In a roller-delayed blowback system, the bolt uses kinematic constraints, which are made up of a combination of a roller (or rollers) and a locking surface. As the round is fired and the bolt moves rearward, the force required to move these rollers from the recesses in the locking surface keeps the action closed long enough for chamber pressure to drop to safe levels.
The grooves act as the locking surface for the rollers, and the rollers create a mechanical delay with the bolt. As the pressure from the fired cartridge dissipates, the roller rolls out of the groove to allow the bolt to continue rearward, ejecting the empty case and cocking the hammer. Then, the recoil spring pushes the bolt forward, stripping the next cartridge out of the magazine and chambering it for the next shot.
Pros and Cons
So now that you know the difference between the two blowback systems, you are probably wondering what the advantages and disadvantages of roller delay versus direct blowback systems are.
The advantages of a direct-blowback system are utter and complete simplicity with fewer moving parts. It is also extremely easy to maintain. On the flip side, this type of design requires a large, heavy bolt and more perceived recoil when that mass is moving back and forth during cycling.
The advantages of a roller-delayed locking system is reduced bolt mass through the application of the roller lock, resulting in lower perceived recoil and very smooth cycling. However, it is a more complex design with more parts.
What’s Better: Roller Delayed or Direct Blowback?
The question isn’t if one type of blowback system is better than the other. The real question to ask is which 9mm blowback system is better suited to your needs. If you cut your teeth on the AR platform and are most comfortable with it, then a direct-blowback system like with the SAINT Victor 9mm Carbine is an ideal option.
The direct blowback AR-15 operates the same way as the direct impingement rifle cartridge system. The charging handle, selector switch, and magazine release are all in the same place. Plus, if you have DIY running through your veins, the AR platform is easily customizable. From rails, sights, pistol grips, stocks, and braces, there is an embarrassment of options in the AR platform. However, if you’re looking for something a little different, then the roller-delayed blowback is a great option.
Of course, if you can’t decide which one to buy, you could just get both. Just get ready for some blowback because if you went over budget!
Editor’s Note: Please be sure to check out The Armory Life Forum, where you can comment about our daily articles, as well as just talk guns and gear. Click the “Go To Forum Thread” link below to jump in!
Join the Discussion
Featured in this article
Read the full article here
