Not all blowback action airguns are created equal
Looking inside today’s latest blowback action semi-autos
By Dennis Adler
When I was a kid there were no semi-auto blowback action air pistols. In fact, until I was almost 53 years old there were no semi-auto blowback action air pistols. Today there are a lot of them, and some have evolved into such accurate reproductions that the only thing separating them from their cartridge-firing counterparts is what comes out the end of the barrel. To achieve that level of authenticity in design and operation, not only the exterior of the pistol has to be correct, but for some models, what goes on inside has to be nearly the same as well.
What is blowback action?
Blowback action is, to paraphrase Sir Isaac Newton, the equal and opposite reaction to an action, in this case the energy produced by the cartridge (or force of the air in the instance of a CO2-powered semi-auto), pushing directly back against the mass of the slide, propelling it rearward and compressing the recoil spring. When the slide reaches the end of its rearward motion, the recoil spring decompresses and drives the slide forward. In a blowback action (or short-recoil locked breech) cartridge pistol, the rearward motion of the slide also extracts the spent shell casing and either re-cocks an external or internal hammer or striker, and then strips a fresh cartridge from the magazine and chambers it while returning forward to the closed and locked position. With the exception of ejecting a spent (empty) shell case, the blowback action of a CO2 powered semi-auto air pistol is essentially the same; action and reaction.
Since the firing of a .177 caliber steel BB doesn’t generate sufficient energy to drive the slide rearward and compress the recoil spring, a portion of the CO2 is channeled into the firing mechanism to simulate the energy generated by a gunpowder discharge, and this is what drives the slide back. It’s also why you get fewer shots with a blowback action semi-auto, since each shot requires the CO2 capsule to power two functions, sending the BB downrange and operating the slide. As a result blowback action air pistols generally have lower velocities than non blowback action semi-autos as well. It’s a small price to pay for an air pistol that looks and operates like a true cartridge-firing handgun.
Blowback action is the basic design used in the majority of small caliber pistols almost since their invention. Most also use a similar internal design with the barrel permanently affixed to the frame and surrounded by the recoil spring.
In operation (regardless of being a cartridge gun or a blowback action airgun) the outer dimensions of the recoil spring are slightly greater than the barrel opening in the slide, and thus when the slide is driven back by firing the gun it takes the recoil spring with it. The spring compresses until the slide hits its stop and the spring decompresses and drives the slide forward again. This design is used in one of the greatest blowback action semiautomatic handguns of all time, the Walther PP, PPK and PPK/S.
To illustrate this I have disassembled a Walther PPK/S .380 ACP, and an Umarex Walther PPK/S. Both disassemble exactly the same way, look the same disassembled, and technically, operate the same way. In the image of the Walther PPK/S and Umarex Walther PPK/S disassembled, both guns reveal the same interior design. To fieldstrip the Walther pistols, begin by removing the magazine, pulling down on the front of the triggerguard to disengage it from the frame, and then draw the slide to the rear, lift up and over the hammer and pull it forward off the frame. While this process is identical in both the airgun and the .380 ACP model, it is not recommended for the Umarex PPK/S since there are parts that are pressed into place, and you need to be certain that they are kept in position when reassembling the gun. But the point is, this is a true blowback action design, and altogether different than the locked breech design used for the latest M&P40 .177 caliber semi-auto as well as the Sig Sauer P226 X-Five .177 caliber blowback action semi-auto.
While every blowback action semi-auto air pistol works on the same principle as the Walther PPK/S, they do not all look or function internally the same as a traditional blowback action pistol, some are actually much closer in design to the short-recoil locked breech design developed by John M. Browning for the Colt Model 1911 and later modified by Browning to use a solid camming lug (linkless cam design) introduced on the Browning Hi Power in 1935. This is the same design (or variation of) that is used today for the majority of medium to large caliber semiautomatic handguns. And it also applies to a handful of the latest “blowback action” CO2-powered semi-auto air pistols!
Short-recoil locked breech design
The best example today of this marvel in airgun design is the Umarex S&W M&P40, which is not only visually, but functionally, a short-recoil, locked breech design. The best way to show this is the comparison between a .40 S&W M&P and the M&P40 air pistol disassembled to show their respective polymer frames, internal mechanisms, slides, barrels, guide rods and recoil springs.
Although the .177 caliber M&P40 is a blowback action air pistol, the design is actually a locked breech short-recoil operated system (as it is on the cartridge-firing M&P models). The barrel breechblock (shown in the view looking down on the M&P40 air pistol and .40 S&W models) actually disengages from the slide during recoil and tilts down as the slide moves back (conversely the muzzle tips up slightly during this action). As the slide comes forward and closes the barrel tilts back and reengages the slide, locking the gun into battery.
On the Sig Sauer P226 X-Five, which also uses a short-recoil, locked breech operating design, the guide rod, recoil spring and barrel can be removed from the slide, since the guide rod on the Sig air pistol actually locks into the barrel lug rather than being screwed down as on the M&P40.
To fieldstrip the M&P40 airgun the same steps are taken and when disassembled it looks like a modern short-recoil locked breech pistol with a polymer frame and fire control housing. Note the accurate barrel, guide rod and recoil spring design used for the air pistol. Any further field stripping of the M&P40 airgun is not necessary and removing the guide rod, recoil spring assembly and barrel from the slide are different than the cartridge-firing version, as the guide rod is screwed into the barrel lug, rather than locking against it like the cartridge model.
Comparing the design used for the Umarex S&W M&P40 to a traditional blowback action is the same as comparing the actual guns. These latest models, like the M&P and Sig Sauer, take blowback action air pistols to an entirely new level of authenticity.
A word about safety
Blowback action airguns provide the look, feel and operation of their cartridge-firing counterparts and this is one reason why they have become so popular. Airguns in general all look like guns, blowback action models more so, and it is important to remember that the vast majority of people can’t tell an airgun from a cartridge gun. Never brandish an airgun in public. Always, and I can never stress this enough, always treat an airgun as you would a cartridge gun. The same manual of operation and safety should always apply.