Poorly Airsporter Mk6, 0.22"

[ggggr]

I am not a "tuner" and only tinker. The only time my rifles have been chrono-ed is when a friend brought his. Having read a few things on here about tuning, it seems that using a Meteor sized O ring helps with power and bedding in---although a friend had a Mercury with a very old O ring that was "hot" until he cut the mainspring.
I'd try to push the the piston and piston head, without the O ring into the cylinder and see if there are any tight spots. If there are not, then I'd try the Meteor sized O ring and the new mainspring and maybe the old mainspring if it is not too bad, after that.
If the tap is ok and there are no really tight spots in the barrel, I would be thinking is the end of the cylinder leaking like hapens on Weihrauchs, although I've never heard of it on an Airsporter but had it on Webley Hawk.
I bought a rough Mk5 off here a good few years ago and that had the siezed nylon pisotn head. I just cleaned it up, fitted a new O ring and found an old mainspring that I liked the "feel" of for cocking and plinking. That was doing just over 8.5ft lb and was lovely for plinking.
Good luck with it.

[PhatMan]

Ken,

WRT Superdomes

Ta

Have fun & a good weekend

Best regards

Russ

[PhatMan]

ggggr,

Ta

I will get some Meteor O-rings and have a play

The Mk6 now cocks and shoots very smoothly - it is a bit lacking on the velocity side of things

If I could get it up to ca. 520 - 530 fps, then I would be happy

Have fun & a good weekend

Best regards

Russ

[Benelli B76]

ggggr,

Ta

I will get some Meteor O-rings and have a play

The Mk6 now cocks and shoots very smoothly - it is a bit lacking on the velocity side of things

If I could get it up to ca. 520 - 530 fps, then I would be happy

Have fun & a good weekend

Best regards

Russ

Russ from your previous posts I would think the O ring is too tight a fit. I did not give you a size because I have loads of O rings and depending how deep the groove is machined I use different ones to match. The O ring should be very slightly proud of the piston head. Too much where you have to force it in the cylinder drops the power.

Baz

[PhatMan]

Baz,

Ta

Yup - the fitted OD of the O-ring is 28.5 mm.

I don't know what the ideal crush for O-rings is for use with air-rifle pistons - I would suppose that it would be say 0.1 - 0.2 mm ?

On fitting, the O-ring bulges out of the cocking slot, so is obviously far too big

I did try a smaller O-ring that I had knocking about, but that leaked.

I will get some 'likely candidate' sizes of O-rings and give them a try.

Have fun & a good Sunday,

Best regards

Russ