Roller Delayed Blowback System: A Detailed Look

Firearms platforms have varying operating systems. With quite a few of those systems on the market, it can get confusing trying to understand and differentiate among them. If you’re a fan of Heckler and Koch’s MP5 or simply curious about the roller delayed blowback system, we’re here to help. Consider this your primer on all things roller delayed blowback: what it is, how it works, and why you might or might not want one.

roller delayed blowback chart
Look confusing? It doesn’t have to be. (Photo credit: SOFREP)

What is the roller delayed blowback system?

Certain semi-automatic firearms have a blowback system, and within that broad term, there are quite a few sub-categories. One is the roller delayed blowback system which is found in guns like the Heckler and Koch MP5, Heckler and Koch G3, Korth PRS, and Mauser Sturmgewehr 45. From a simplified standpoint, the roller delayed blowback system utilizes recoil to cycle the action by way of rollers located at either side of the bolt. The rollers are what create the delay, slowing down the process until the pressure equalizes. Of course, there’s a bit more to it than that.

roller delayed blowback system image
An example of the roller delayed blowback system. (Photo credit: Heckler and Koch)

How does the roller delayed blowback system work?

First, let’s clear something up: this isn’t a locking system. It’s not uncommon to hear it mistakenly referred to as a locking system, but that is inaccurate. The roller delayed blowback does exactly what its name suggests: it delays.

As you can see in the image above, the rollers are on either side of the bolt head. The rollers are the components that create the delay in cycling, slowing things down until the pressure generated by live fire drops to a “safer” level. When a shot is fired and super-heated gases create significant pressure, the rollers help maintain a seal, delaying the action until enough of those gases escape to create a safer level, at which point the rollers allow the action to finish cycling. This all happens in the blink of an eye.

What would happen if the rollers didn’t delay the cycling of the bolt? Escaping gases at a too-high pressure could blow back into the gun and seriously damage not only the action itself but the shooter. It’s important that the pressure level drops first. In reality, it’s a fairly simple system.

roller delayed blowback system
A look at a roller delayed blowback assembly. (Photo credit: Ronins Grips)

What are the benefits of the system?

There are specific reasons some firearm manufacturers use this system. It typically creates a lighter-weight platform than those that use other types of blowback. Saving weight might not sound like a big thing, but even shaving off ounces here and there is valuable, especially in battle rifles. But aside from the weight-saving potential, use of the roller delayed blowback system can facilitate the use of higher-pressure, larger cartridges. That doesn’t mean all roller delayed blowback guns are chambered in big bores, because they’re not, only that the system is designed to withstand and manage greater pressure.

Other pros of the roller delayed blowback are the fact that it’s frequently more affordable to manufacture and provides reliable, consistent cycling. Keep in mind that the most common firearms made with this system are submachine guns and battle rifles that must be capable of maintaining a higher rate of fire and use than the average guy’s gun.

What are the downsides of the system?

The most obvious downside might be the fact it tends to be dirtier than some others. It also has more moving parts and is more complex than some designs which some people will see as having a higher risk of breaking or failing. That thought process isn’t totally wrong, either; as the gun is used, the rollers can wear down, eventually losing their ability to seal well and causing issues. Of course, that requires an incredible amount of use.

Another detail of this system that can certainly be seen as a negative is the fact that using this system can require additional manufacturing steps and details to be added to the firearm in question. That circles back to its complexity, which is also simple in its execution despite the moving parts and science behind it.

heckler and koch p9
The Heckler and Koch P9 is a roller delayed blowback handgun. (Photo credit: By Hecklerfan via Wikipedia)

Are there any roller delayed blowback handguns?

Most roller delayed blowback handguns are rifles and submachine guns, but there are a few handguns that have been made with the system in place. These include the Heckler and Koch P9 and the Korth PRS. The P9 was designed in the 1960s as the company’s first roller delayed blowback pistol. It’s offered chambered in 9x19mm Parabellum, 45 ACP, and 7.65x21mm Parabellum. There were a few variants of the P9 made and for a time the U.S. Navy used the P9S, suppressed.

How common is the system?

This system isn’t exactly common, not when you compare it to the many other designs on the market. It was originally created by Mauser for use in the Gerat 06H, which eventually became the Sturmgewehr 45. This involved extensive mathematical equations and serious technical work, and the end result was a system that’s admired by a lot of gun owners despite it not being common use.

According to en-academic, the progression of the system can be summarized:

The Mauser technicians VorgrimmlerLöffler and Kunert perfected this mechanism between 1946 and 1950 when they designed the French AME 49 at Atelier Mécanique de MulhouseThe first fullscale production rifle to utilize roller delay was the Spanish CETME followed by the Sturmgewehr 57 and the Heckler & Koch G3 rifleThe MP5 submachine gun is the most common weapon in service worldwide still using this systemThe P9 pistol is one pistol that uses rollerdelayed blowbackhowever the Czech vz52 is rollerlocked.

If you’d like a visual, perhaps one of the best video explanation of the system comes from Ian McCollum of Forgotten Weapons. Check it out below:


If you own or are considering getting a gun with a roller delayed blowback system it’s a good idea to have a better understanding of how it works. And even if you don’t have one, it’s cool just knowing a little bit more about firearm history and how things work.

Kat Ainsworth Stevens is a long-time outdoor writer, official OGC (Original Gun Cognoscenti), and author of Handgun Hunting: a Comprehensive Guide to Choosing and Using the Right Firearms for Big and Small Game. Der Teufel Katze has written for a number of industry publications (print and online) and edited some of the others, so chances are you've seen or read her work before, somewhere. A woman of eclectic background and habits, Kat has been carrying concealed for over two decades, used to be a farrier, and worked for a long time in emergency veterinary medicine. She prefers big bores, enjoys K9 Search & Rescue, and has a Master's Degree in Pitiless Snarkastic Delivery.

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