Spring Gun Tuning

[Mike95]

I do not pretend to be an expert, but the more rifles I strip and the more I read (particularly Cardew, the Airgun from Trigger to Target), the more I realise just how important it is to size the piston seal to the cylinder. The fit between seal and cylinder seems to be the major factor with older guns, in establishing the ME. I recently stripped and cleaned/relubed an old Meteor with an "O" ring seal and it did not occur to me to try and size the "O" ring. The "O" ring was in good condition and I gave it a smear of molypaste before reassembling. The gun is fireing fine but is low on power. The spring is fine and the relube is fine, therefore must be the seal! I cannot see a nitrile/butyl "O" ring sizing down very much and Ged Finn on another thread suggested possibly fitting a smaller diameter "O" ring. Presumably an "O" ring could be sanded down. The Cardew book demonstrates just how critical the sliding fit between seal and cylinder is, but unfortunately this is just guess work without equipment to measure the sliding fit. Too tight and you have limited power...too slack and you have the same result. The joys of springer tuning!

Mike95

[electric sheep]

Lower ME guns work better with parachute or semi parachute seals with sliding fit but FAC and higher ME springer's work more efficiently with higher swept volume solid seals with a tighter fit. Both need a good moly paste and a cross hatched compression wall to wet edge the seal to wall contact. It is not unusual to have a 30% range of power with the same spring set and different seals.