Fixed Barrel Semi-Auto?

[mony]

How goes the quest for a fixed barrel semi-auto? I have read of pistol makers trying to perfect such a beast, but it has been some time. I know of the Luger, and maybe there are more. Not being the most mechanical guy in the world, but having viewed the STI animation till my eyes watered, I wondered what is the biggest hurdle in developing such a handgun?

[James K]

I assume you are talking about a pistol for a powerful cartridge; obviously there are many fixed barrel auto loaders for .22, .32, and .380 as well as 9x18 Police and 9x18 Makarov. There have been fixed barrel pistols for 9x19 (9mm Luger), including the old Astra 400, 600 and 800, the H&K P7, the Steyr GP, the gone and unlamented Rogak, the High Point, etc. High Point even makes blowback pistols in .40 S&W and .45 ACP.

The Luger has a fixed barrel only in that the barrel is attached to the recoiling receiver; it is still a locked breech, short recoil action, not a blowback.

The "hurdle" is pressure. Like any firearm, the auto [loading] pistol has to be made with a breech that will contain the pressure generated by the gas from burning powder. In, say, a bolt action rifle, the method is obvious. But in an auto pistol the designer wants the breech to open automatically so the empty case can be extracted and ejected and a fresh round inserted in the chamber.

The problem is that if the breech is allowed to open while the pressure is still high (before or even just after the bullet leaves the barrel), the cartridge case can come out far enough to expose its weak sides and it will blow apart, wrecking the gun and possibly injuring the shooter.

So the idea is to prevent that. In what is called a "blowback" action (low power pistols), the inertia of the breechblock (usually a slide, but it can be a bolt like a Ruger .22) is enough to hold the case in until the pressure drops. The case is allowed to just blow itself back out of the chamber (hence the name "blowback"). The extractor is not needed except to remove an unfired round, and blowback pistols have been made without an extractor.

In high power pistols, the usual method is to lock the barrel and breech together by some means until the pressure drops. That type of pistol operates by recoil, not pressure. In a Model 1911, for example, recoil begins as soon as the bullet starts to move, and while the bullet is moving down the barrel, the barrel and slide are recoiling together. As the bullet leaves the barrel, the barrel and slide are unlocked, the slide continues back on its own momentum to extract and eject the empty case and then comes forward under spring pressure to pick up a fresh round and again lock with the barrel.

There have been high power pistols made to operate using gas, but the majority are locked breech, short recoil systems as described above.

So how does High Point get away with a blowback action for high pressure cartridges? Remember that about a blowback pistol depending on the inertia of the slide to keep the pressure contained long enough? Well, inertia depends on mass (weight). Most designers didn't want to make a slide of enough mass to contain high pressure, since that would make the pistol awkward, heavy, and hard to hold. High Point did.

Jim

[w_houle]

Another interesting fixed barrel design that's a delayed blowback is the Remington 51. Don't know why no one has resurrected the design, but it sure is interesting

[mony]

Mr. Keenan, thanks for the response. It was exactly the type of explanation I was looking for. It makes so much sense and seemed obvious once you explained it. This is why I joined this site. Thanks for the lesson.

[James K]

Hi, Mony,

You are very welcome. Believe me, you are not the only one to be confused. I once saw a CAD design for a semi-auto rifle firing .308 Winchester. It is fortunate that the young designer never got beyond the CAD stage, since the CAD program knew nothing about pressure and couldn't tell him his simple blowback design would blow apart and probably kill him if he tried it.

Hi, w houle,

The Remington design was by John D. Pedersen, who was Remington's in-house designer for many years and who also designed the famous "Pedersen device." That Model 51 design is interesting, but quite complex, as most of Pedersen's designs were.

Great advantages were claimed for it, but in fact the reason for that design (and the designs of the Savage, S&W, Davis, and other pistols of the time) was that the simplest design, a solid breech block as part of the slide, had been patented by a fellow you may have heard of, John M. Browning, and assigned to Colt. As long as that patent was in effect, the other designers had to figure out a way around it, and Pedersen's design was one way.

Jim

[melchloboo]

Here is an interesting concept, not sure what the status is:
http://www.m1911.org/hogueavenger.htm

[Scorch]

Interesting. My first thought when I looked at the diagrams was "it works like a P38", and in fact they say as much in the write-up. I don't know how great that would be, but it looks interesting.