Hold the Blowback?

[Nee Zee]

I am contemplating an experiment, but would like the opinion of the experts here before trying it...

I have a Sig Sauer P226 blowback CO2 pistol and was thinking, what if I were to rig up a way to hold the slide and keep it from blowing back, would that increase the power level by directing the full CO2 blast towards the pellet? I imagine you'd gain a significant increase in FPS. 

This would of course make it single action only since the hammer would need to be cocked manually, I'm ok with that. But could this modification tuin the pistol?

Looking forward to opinions, thanks.

[subscriber]

Neil,

This is an indirect answer, as I don't know the detail of how your CO2 pistol applies gas pressure to drive the slide.  The thread linked below is of a forum member making his own semi-auto air pistol:
https://www.gatewaytoairguns.org/GTA/index.php?topic=216727.0  His pistol required that gas pressure be applied to an additional area, rather than just the probe area (about the same as the projectile), or not enough force would be generated to operated the gun.  If you pistols' visible hammer is the functional hammer then the force driving the slide is applied in a different manner.  Probably using the recoil spring guide as a piston.

In any event, because the slide or bolt is much heavier than the pellet or BB, the action opens much more slowly that the projectile travels down the barrel.  In other words, the increase in active bore volume during firing is mostly due to projectile motion, rather than the action opening.  Ditto for the projectile leaving the muzzle before the breech leaks gas.

What I am suggesting is that your pistols' velocity is likely not going to increase very much, if at all. It should be easy enough to find out:  Shoot a few shots in semi-auto over a chronograph.  Wait a few seconds between shots for the gas to warm up, else the velocity will drop because the CO2 is cold from evaporation, and the gas pressure would keep dropping between fast shots.

Now, with the pistol in shooting state and the safety on.  Wrap the slide and frame around in several layers of adhesive tape.  The stronger the tape the more likely you can stall the slide completely, but the harder the tape is to remove.  Shoot over the crono and compare the velocities.

If I had a pistol like yours I would be tempted to use my free hand to grip the slide and frame together, but I would suggest you derive a reversible method to do this that carries no risk to your skin.  Anyway I think that the semi-auto mechanism uses a lot of gas to cycle, but rather than reduce the velocity of the projectile directly, it does so by using a lot of extra gas, and increasing the time you need to wait between shots, before the gas pressure is up to full pressure at that ambient temperature.  So, you get fewer normal velocity shots per gas cartridge because of the slide action; rather than a reduced velocity on a fresh CO2 cartridge.

The folks in the CO2 "air" gun section probably already know the answer to your question.  This
"gate" may not generate the required visibility to the folks who shoot CO2 pistols.   I will PM some, pointing at this thread to see if they have something to add.

[subscriber]

See this thread, Neil:  https://www.gatewaytoairguns.org/GTA/index.php?topic=213006.msg156516413#msg156516413

[Blowpipe Sam]

I surmised that holding the bolt closed and preventing blowback would have a beneficial effect on the velocity of my Air Venturi/Springfield Armory CO2 M1 Carbine.  This was not the case.  The configuration of the valve and the blowback mechanism prevent this.  I don’t know how the blowback on the Sig works but I expect it is similar to the AV/SA M1 in principle.  The M1 will not fire if the bolt is prevented from moving backwards.

[TorqueMaster]

I have one of the KWC 1911 look-alikes -- just tore it down to see how it works. 
It appears when the hammer trips, CO2 is simultaneously directed behind the BB and into a small piston that drives the slide rearward. 
It *appears* to me if one were to prevent rearward movement, more CO2 would be directed towards the BB.  Will the piston assembly "rapidly disassemble" if you do this?  I don't know -- probably not -- but I'm not going to find out.

The better angle to ask is -- what FPS are you getting?  The barrel is only about 4.0 inches long, and there's only so much FPS CO2 can create in such a short barrel.  I'd say if you are getting 350-400FPS, there's not much more to be had by preventing the blowback.   The main advantage might be *more shots* per CO2 cart.

The blowback model claims "300-330 fps" and iirc about 40 shots.
A similar non-blowback claims "up to 425 fps." 

I'd expect 40-50 shots out of a fast non-blowback, I've seen 80-100 out of one with less velocity.

Either way, it's pretty anemic -- you aren't going to get much more than 450fps out of it no matter what you do.  I'd blow $20-30 on a non-blowback Daisy or Crosman BB pistol, tinker with that, and enjoy the Sig for what it is, not try to fix what it isn't.

[JPSAXNC]

Stopping the slide from moving probably won't increase power. If you could block off all co2 losses that would help, you want the gas pushing on the pellet, not going anywhere else or leaking from anywhere. The increase wouldn't be very high because unlike compressed air co2 is constantly expanding, so it's still providing a lot of force even with losses.

[Nee Zee]

Thanks guys for the replies. To be honest, I don't shoot enough to justify buying a chronograph, but I do like to tinker. Yes, the Sig is pretty wimpy power-wise, but the blowback makes it alot of fun to shoot. I have done the barrel fix seen on utube which improved accuracy.

It is a very simple mechanism, but I haven't found any piston, not really sure how the slide gets kicked back. It does have a real working hammer for single action, so I figured maybe I could squeeze some extra FPS by locking down the slide.

But maybe Bob is right and I should just "enjoy the Sig for what it is" and it is alot of fun to shoot, and a beautiful all metal replica that is so heavy it can stun an ox!