Radial Delayed vs Direct Blowback – Hot Takes

Pistol caliber carbines have experienced a crazy resurgence and have cemented themselves into the mainstream firearm industry. Why not? They are cheap to shoot, easy to suppress, and often allowed at indoor ranges. They can also be ultra-compact and lightweight. They often take popular pistol magazines and can be a ton of fun! Most operate on a direct blowback principle. It’s fairly common and has been around since early handguns and the first SMGs. A company called CMMG leaked out something called radial delayed blowback that aims to change the market.

Direct blowback might be the old standard, but in recent years both PCCs and SMGs have wandered away from the classic method of operation. Direct blowback may be simple, but it has some downsides we’ll examine a bit later. While short gas pistons and roller-delayed blowback is cool, it’s also expensive. Look at the price of MP5s and their clones. They are ancient guns these days but still demand a premium.

bolt differences
Notice the major bolt differences between the two guns.

A radial delay system isn’t as simple or as cheap as a direct blowback design, but it’s a good deal cheaper than other blowback systems, and we’ll dive deeper into that a bit later. Today we are going to do a complete breakdown of both direct blowback and radial delayed blowback and examine the pros and cons of each so you can make a more informed decision about your building and buying options.

How does direct blowback work?

It’s arguable how far direct blowback mechanisms have existed. Some patents going back to 1856 use direct blowback methods to make loading cannons easier. Bernard Fasoldt patented a blowback mechanism for a single-shot rifle in 1876. In 1883 Hiram Maxim patented a blowback-operated rifle. It’s not a new idea, and it’s been around so long because it’s so simple and functional.

direct blowback bolt
The direct blowback bolt is as ugly as it gets.

Direct blowback guns use an unlocked breech, which means nothing keeps the bolt pressed against the barrel outside of some form of recoil spring. The system uses the force generated by the firing of a round to operate the weapon. When the weapon fires, the projectile travels down the barrel propelled by the hot gas generated by burning gunpowder. As the projectile moves forward, the case is simultaneously being pushed rearward by the same gas.

The case is pressed against the bolt. The bolt has to be capable of resisting this rearward pressure until the projectile leaves the barrel. This often involves a combination of a heavy bolt, heavy buffer, and heavy recoil spring.

Eventually, the pressure pushes the bolt rearward with enough force to overcome the recoil springs and drive the bolt far enough back to cycle the weapon. This involves extracting and ejecting the brass case, resetting the hammer, and loading the next round from the magazine. As the bolt reaches the rear of its travel, it has slowed down enough to be pushed forward once more by a recoil spring.

How Does Radial Delayed Blowback Work

The history of radial delayed blowback is rather short. CMMG introduced the concept in 2017 in the Mk 45 Guard Rifle. The system still uses a blowback design but no longer uses an unlocked breech. A radial delayed gun uses a series of lugs attached to the bolt head, much like a 5.56 caliber AR-15. These lugs are cut at a slight angle and lock into the chamber of the rifle.

radial delayed bolt
If you didn’t know better you’d swear this was a 5.56 bolt.

When a shooter fires the weapon, the projectile flies forward, and the case wants to fly rearward and open the bolt. Before the bolt can be opened, it has to be unlocked via rotation force. As the backpressure pushes, the bolt rotates slightly but unlocks it from the chamber. The bolt is now free to move rearward, extract and eject the casing, reset the trigger, and pick up the next round on the way back.

The rotational force creates enough of a delay in the action opening that the projectile can leave the barrel safely. It eliminates the need for a heavy bolt, buffer, and recoil spring.

Upsides and Downsides to Direct Blowback

Blowback-operated guns tend to be super simple in design. They aren’t ammo picky, they don’t mind suppressors, and they are much more common. It’s such a simplistic design that it’s tough for anything to go wrong. The bolt shoots rearward, completes its cycle of operations, and is ready to get back on target. The commonality ensures it’s the cheap means to build or buy a PCC.

The downsides are abundant. The most obvious is excessive recoil. You are dealing with every bit of recoil a pistol cartridge can offer. A 9mm PCC throws about the same amount of recoil as a 5.56 carbine. That’s not a lot, but it seems excessive for a pistol cartridge. The weighty bolt and buffer don’t help much either and often end up contributing to the violent recoil impulse.

two AR9 rifles
Both rifles are a ton of fun.

The stronger recoil springs also ensure it’s hard to rack a round into the chamber. Direct blowback guns tend to be dirtier, but to be fair, they tend to run just fine when dirty. Another issue is larger calibers. While direct blowback 45 ACP and 10mm guns exist, they are rare because it’s tough to do it right. Oftentimes anything larger than 9mm will be tough to find.

Upsides and Downsides to Radial Delayed

Radial-delayed guns give you super soft recoil. They barely move between shots, and they are what a 9mm carbine should feel like. They are also much lighter since a heavy bolt and buffer aren’t required for them to function correctly. They are easy to rack as well. Radial delayed rifles also easily chamber cartridges like .45 ACP and 10mm.

CMMG and Basic AR9
Blowback guns tend to have more magazine options and this model uses the MEAN Arms EndoMags.

In fact, the radial delayed design was originally specifically aimed at making reliable, safe, and comfy big-bore pistol caliber carbines. Over time it’s adapted to numerous calibers, including 9mm and 5.7x28mm.

Radial-delayed guns can be a bit more sensitive to suppressor and ammo types. CMMG includes a weight kit to make the gun easier to use either. These weights attach to the BCG and allow you to fine-tune your performance. Another downside is that, so far, radial delayed guns are only available in AR platforms.

My Take

I own guns in both direct blowback formats and radial delayed designs. The radial delay is more enjoyable to shoot. I use my MkGs rifle in competitive shooting because I want that extra edge that less recoil offers. With direct blowback guns, I appreciate being able to own platforms other than the AR, like the CZ Scorpion. For serious tasks, I’m taking the radial delayed design, but I still have tons of fun with the direct blowback guns out there.

What’s your take? Share below!

Travis Pike is a former Marine Machine Gunner and a lifelong firearms enthusiast. Now that his days of working a 240B like Charlie Parker on the sax are over he's a regular guy who likes to shoot, write, and find ways to combine the two. He holds an NRA certification as a Basic Pistol Instructor and is probably most likely the world's Okayest firearm instructor. He is a simplicisist when it comes to talking about himself in the 3rd person and a self-professed tactical hipster. Hit him up on Instagram, @travis.l.pike, with story ideas.

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