Fine tuning a Classic Pump Mag On/Off

[Motorhead]

My Classic mag works just fine, BUT .....

The sound at time of shot varies with how I squeeze trigger. Sometime marker fires with a crisp "POP", other shots a "POP HISS" ( Velocity however stays consistent )

* I know this hiss is the gas refilling the dump chamber.

But being this is a PUMP altered marker and after a shot the sear is not catching the bolt and the On/Off should not allow refilling of the dump chamber yet until fully cocked.

SO, if I am hearing a hiss right after the shot one would think the On/Off timing controlling gas refill is happening a tad premature ?

Are there SHIMS that can be fitted between the TOP o-rings and valve body that would move the rings slightly closer to pin ?

Would this not alter the timing like a longer pin would do ?

Thanks,
Scott

[flyingpootang]

Scott, What type of on/off are you using am/mm, RT, or ULT? Also to diagnose if its the on/off hold the trigger down. If the hiss goes away then your on/off is leaking.....

[athomas]

Yeah, it could just be a bad on-off top oring.

[Motorhead]

Does it with either the stock On/Off or a .750" pin RT On/Off

Holding trigger makes no noise ....
* The noise of "HISS" follows the shot pop as one continual noise ... Popsisss

I did some screwing around with it over the weekend and could eliminate the HISS by using a worn out bolt spring, But result of that was a longer and firmer cocking action getting bolt to reset.

[flyingpootang]

Scott, Could you list exactly what valve, on/off and (classic, rt or ULT), that your using....Thanks

[Motorhead]

R/F SS stock body
Am/Mm stock rail & sear
Classic valve (Matched halfs & rebuilt)
Newer style on/off with radial hole brass spacer (Actually was stock in this newer valve)
AGD level 7 foamee bolt

* Trigger to sear push rod has @ .030 gap when cocked.


What I am guessing is that when using a softer worn out bolt spring, the reset sequence that in case of a pump has the bolt pushed back against the wave spring not as far and in turn the rocking of the sear is moving the on/off pin less.
Use a stiffer bolt spring and sear is SOOOOO close to catching, the sear rocks a tad more and on/off pin a tad more as well.

It's on/off pin timing to some minor degree, but clueless how to address it ?

[athomas]

Try a new powertube oring and/or a shorter powertube spacer. You are probably experiencing a tiny leak out the powertube following the bolt return. Using the shorter powertube spacer will provide a more positive seal.