78 on .177?

[Doc Sharptail]

Kind of curious as to how the factory detunes the .177 versions of the 78's.

I'm looking at a hpa build for one, and ideally it would be at lower pressures. I am tempted to use just the factory CO-2 tube and the brass bulk fill fitting from S&A for it. The target is the upper 400's- hopefully 470-490 with the 10 gr CR Ultra-mags.

I'm guessing that something as throttled back as that won't require a lot of volume? I won't need lengthy shot strings. The gun will be for an after work tension reliever, and high performance velocities certainly won't be a requirement...

Regards,

Doc Sharptail

[rsterne]

I tried HPA on a stock QB78 in .22 cal, and I got 34 shots at 10.7 FPE.... Since a non-PAL .177 would only be about 4 FPE, you should be able to double that count with nothing more than restricting the transfer port.... I filled to 1600 and shot down to 600 psi with only a 10% ES....

Bob

[AirGunEric]

The factory doesn't detune the .177's- if someone is selling them they should have done the detuning themselves. The easiest way to do it is to cut the hammer spring or put a sleeve in the valve to take up volume.

[SeanMP]

To get my AR to shoot a 525 flat string took a .058" transfer port.

[rsterne]

Sounds about right in .177.... How many shots on a QB78 tube, and from what pressure to what?....

Bob

[SeanMP]

Flat string was about 35 shots from 1500 to 800psi

But I only allowed +/- 10fps

[Doc Sharptail]

It looks like it will be a relatively un-complicated endeavour from what I've been reading.

I've been noticing a trend in my notes- "heavy for caliber" pellets seem to tend to lower ES's in my pumpers and more recently, hpa tube. It's been a little harder to make a determination on co-2- the 12 gram caplets are temperature sensitive, and don't hold enough gas to make serious comparisons in .22. I still have a lot to learn.

I'll likely be using the AR-20-78-A tube. The de-gassing key seems to be an attractive option for what I want to do.

Regards,

Doc Sharptail