Tuning advice wanted.
I know a lot of you guys here tune your guns.
Being lucky enough to live in a free country this often seems to consist of maximising the power without losing accuracy.
Here in the UK we have different problems. Unless you have a firearms licence, we are restricted to a maximum power of 12 foot pounds energy. To us, tuning a gun is about maximising the shot-to-shot consistency, flattening the power curve and getting the most “good” shots on the flattest part of the power curve per air charge.
It seems to me there are 3 variables on the Air Force/Gunpower system.
The pre-load on the hammer spring (we don’t have the power adjustment wheel, we have to use spacers to adjust pre-load)
The top hat position
The pre-load on the valve spring
Any advice on where to start tweaking for best efficiency at UK legal limits gratefully received.
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As consistancy is the aim here,,at sub 12ft/lb,,any slight variation in air delivery will be much more noticeable than at FAC levels.
My top two mods were;
Have the valve stem o-ring conversion done by Leupy to remove the chance of leakeage and reduce noise.
Change the hammer to one which runs on the barrel OD rather than in the frame which again is much more consistant.
All the other tips apply ,,such as good quality/condition 90 duro O-rings in the breech slide,properly lubed with silicone grease,,,minimum hammer lubrication to reduce sticking.I use Dry-Slide throughout.
Finally,,consistant pellet insertion pressure does make a significant difference to MV. I tried useing a plastic pen end to push the pellet well into the barrel end,,,and the MV dropped 😯
You wont be needing to hit the valve hard, so to start you can turn the tp down quite tight. A light hammer with more preload seems to offer best consistancy in that department. I’ve never used a stock valve, so dunno about the valve spring. Fill pressure is down to experimentaion, you gotta shoot it through…
Also fill pressure and hammer weight are part of the balancing act !
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Thanks all.
I had the foresight to order one of Leupy’s hybrid hammers along with his spring, guide and spacers when I bought my first Stealth.
I have a Stealth and a Storm, both second-hand and I don’t know the history but plainly something has been done to the valve on the Storm as it sports one of Leupy’s top hats and there is a little box with the original top hat, valve stem and also the brass part of the valve. Without taking it apart I won’t know for certain but I suppose it is possible it has had the O ring mod.
The Stealth is a .177 and the Storm is currently a .22 but I have an 18″ .177 BSA barrel on order from Leupy. It also came with a Leupy hybrid hammer/spring/spacer/guide set and Drum is making the hammer bearing section of the barrel to suit.
So, screw the top hat down and pre-load the hammer more.
Will give it a try.