Hehe, sorry to derail this for a little bit, but I'm still concerned
How does the bolt moving back close off the valve? You mean, when the bolt moves back, the air passageway that connects the valve opening/output to the bore behind the valve? In that case, I get it. I'll have to try that! Seems like one must be careful though - obviously moving the bolt too much towards the open position could screw things up, such as letting the bolt slide back just as one pulls the trigger, thus closing the valve port off early and decreasing fps.
I know, for a fact mind you
that when it comes to nelsons, having the breach even the smallest bit will reduce fps. But a sniper isn't a nelson, although I must say the reason I've added all my return springs is to, on the ccm make it easier for me to a/t (my pref, that's all), but on the others keep the bore sealed so I don't lose fps. Actually that has been somewhat of a recently development - things changed when I started using hpa 90% of the time over co2 due to local availability/cost. Never noticed a need for the springs with co2, so now this is all making sense... Given co2's low, compared to hpa, rate of expansion, maybe that has something to do with it?
Anyways, thanks for the tips guys!