Rotary Action Autopistols—What Are They, and Why Do You Need One?

The Glock 19 (top) uses a tilting barrel short recoil system while the Beretta PX4 Storm (bottom) uses a rotary locking system.

To learn more about the Beretta PX4 Storm, click this link: https://www.px4storm.com/.

To purchase a Beretta PX4 Storm on GunsAmerica.com, click this link: https://www.gunsamerica.com/Search.aspx?T=PX4.

What is a rotary action pistol, you may ask? And do I need one? Well, just to make sure we are all on the same page, let’s consider what they are. In the world of rifles, where a bolt locks into a barrel or barrel extension, a “rotational” locking mechanism is a common thing. Lugs on the bolt move past other lugs in the chamber, and when rotated, the bolt is firmly locked into the chamber because the lugs can’t move past each other. To separate the two, something has to rotate the bolt to unlock the lugs. Depending on the design, either manual operation or gas pressure unlocks the bolt.

Pistols are a bit different. While a rifle barrel and chamber are (generally) stationary, and just the bolt moves backward to extract a case and load a new cartridge, a pistol barrel (generally) recoils backward a bit along with the “bolt.” Of course in a pistol, it’s not really a called a bolt, but a slide that has a breech face machined into it, so it serves a similar purpose. You might think of a semi-automatic pistol slide kind of like a combination bolt and bolt carrier.

A semi-automatic pistol operates because of a carefully choreographed balance of time and motion. The barrel and slide lock together to create a sealed chamber. After the shot is fired, this chamber stays closed until the conflagration inside chills out a bit, and pressure falls to manageable levels. If the slide and barrel separated at the instant of ignition, you would have all the chaos of a muzzle blast except it would be right around your face and hands, coming out the back of the barrel instead of the muzzle. So, the slide and barrel need to be locked together as the cartridge ignites to keep the chamber sealed. As pressure drops, they can separate so the process of extraction and loading can begin.

Many semi-automatic pistols, like this Glock 19, lock via fit between a square portion of the barrel hood and the ejection port.

The solution that makes a semi-automatic pistol work is a delayed action, where the slide and barrel remain locked together for a fraction of a second. After that, the slide and barrel can unlock and separate safely. Just as with our rifle example at the beginning of this article, the pistol barrel and slide lock together with lugs machined into the barrel and slide. Depending on the “design” of the unlocking mechanism, the barrel may either unlock from the slide by tilting out of alignment, or, in the case we’re going to talk about today, by rotating like a rifle bolt.

The ramped lug on this Glock 19 barrel tilts the barrel down, unlocking it from the slide.

Pistols like Glocks, Springfield Armory XD family members, and Smith & Wesson MP pistols use a short-recoil tilting barrel system to make this work. The energy of the cartridge drives the slide and barrel backward. These two parts are temporarily locked together as the squared back of the barrel locks into the top of the ejection port. A lug extension on the bottom of the barrel eventually catches a locking block in the frame, causing the barrel to tilt downward, thereby unlocking it from the slide. The barrel stops moving backward while the side continues rearward to complete the ejection, cocking, and reloading actions.

The groove in the Beretta PX4 barrel (bottom) causes rotation of the barrel during recoil.

How rotary action works

Rotary action pistols are somewhat rare when compared against more traditional tilting barrel designs. One of the more common and popular of these relatively rare birds is the Beretta PX4 Storm. With a rotary-action pistol, the results are similar, but the method differs. The barrel and slide still remain locked together for a hot second until pressure drops. However, as the slide travels back, the barrel rotates, rather than tilts, to unlock from the slide.

Using the Beretta PX4 Storm as an example, there are several design features that cause the barrel rotation and subsequent unlock from the slide.

First, the barrel locks to the slide in two different places. The front edge of the ejection port and a ledge machined into the inside of the slide both serve to prevent the barrel from moving relative to the slide when the barrel is oriented in the normal firing position. Hold that thought for just a minute…

Here you can see how the central block (below) engages the barrel groove (above).

The captive recoil spring is anchored by a central block positioned under the chamber. This block has a lug that mates with a groove cut into the bottom of the barrel, just under the chamber. The groove is angled so that when the barrel travels over the central block lug, which remains anchored by the frame, the lug causes the barrel to rotate about one-eighth of a turn in place. As the barrel rotates, those two locking points move out of alignment and the barrel releases from the slide. So, like the bolt on an AR or bolt-action rifle, the rotation drives the lugs out of the locked position.

You can see where the barrel locks to the front right edge of the ejection port. There’s a second locking point on an internal ledge in the slide.

The really nifty thing about the design is that it’s not reliant on just that central block lug forcing the barrel to turn as it moves backward. The rifling pattern is cut with a right-hand twist, so as the bullet travels down the barrel, it tends to torque the barrel clockwise from the shooter’s perspective. That clockwise rotation is not coincidentally the same direction of turn required to unlock the barrel from the slide.

Why rotary action?

There are a few theoretical advantages to a rotary action over other designs.

With a tilt-lock system, the barrel physically goes out of alignment with both the sights and the target during the recoil process. Accuracy from shot to shot depends entirely on the barrel moving back into the exact same position relative to the slide and sights as before the recoil action. With a rotary system, the barrel still moves, but it never comes out of alignment with the slide and sights because it rotates in place. In theory, with less moving around, a rotary system may have mechanical accuracy advantage. In reality, it’s probably a moot point. Unless we go out and build pistols of different action types, bolt them to a granite block, then start a bench rest pistol competition at 100 yards, the whole accuracy difference will never be visible in practical applications. There are plenty of pistols with tilting-barrel, link, and rotary actions that are already far more accurate than anyone of us can shoot.

Note how the barrel remains perfectly straight during the rearward movement of the slide. That’s one of the benefits of the rotary system.

The other theoretical advantage is an improved felt recoil experience. Rather than a direct backward action as with a tilting barrel system, the rotary movement bleeds off some energy as the barrel rotates, so, again, in theory, felt recoil is reduced. However, it can result in a sensation of “torquing” of the pistol in the hand.

Here you can see how the muzzle rises during the rearward movement of the slide on a tilting barrel design.

Last, the design lends itself to a lower bore axis relative to the hand. The straight back and forth movement of the barrel allows the top cartridge in the magazine stack to be oriented almost directly behind the chamber. There’s no wasted space between the magazine and the barrel, so in effect, the barrel is lower relative to the frame. You’ll notice that there is hardly any feed ramp on a rotary action pistol because it’s simply not required. Not only does the straight in feed help with reliability, but it also allows for a fully supported chamber. Of course, the lower the barrel is relative to your hand, the less muzzle flip you’ll experience.

And finally, theoretically, it can allow for a lower bore axis than a traditional tilting barrel design, which requires more room below for the dipping movement of the barrel during recoil.

So that’s what rotary action is all about. Is one right for you? I recommend trying one out for yourself to decide. Give it a spin!

To learn more about the Beretta PX4 Storm, click this link: https://www.px4storm.com/.

To purchase a Beretta PX4 Storm on GunsAmerica.com, click this link: https://www.gunsamerica.com/Search.aspx?T=PX4.