'Been there, done that'..., so to speak. I had a great tune on my U2 .25 700 that was shooting 44gr at 980fps with outstanding accuracy and consistent ES of 3fps. Life was good for a few hundred rounds until the o-ring on the shoulder of the valve poppet split! Pulled the rifle down, replaced the o-ring and all was good. A few hundred rounds later, same story..., split o-ring. I've had the o-ring split 4-times with the hammer spring adjuster plug no tighter than the factory setting of flush with the back of the block.Hello,
After I ended banned on UK AG forum for “spamming”, after I directly answered what was my max power achieved with Uragan 2/ .25/ 700mm, I want to share it here for all interested. Hopefully, people here will be more interested than people there
So… I’m playing for some time with my U2, specifically interested in heavier slugs and ELR with transonic velocities, so I can get better BC than usual. After some findings about HS tension screw on factory default settings, I started tuning the balanced valve. My logic was next: if by default HS tension is too high, what would be the balanced valve tune to make maximum out of it? I was thinking like: if I’m not bringing any new stress to valve by doing so…
Btw my only proof of good tuning was ES; if it’s low- I’m good.
Finally, I achieved some respectable numbers with different slug weights and here’s my “middle ground”:
ZAN slugs 37grain@333mps (1092fps) and ES 6. That’s 98 foot-pounds of energy
Obviously, lighter slugs are going above speed of sound, therefore my future research goal is to play with +40grainers, either with CARM magazine or one by one.
Just for further reference, at the end, when I realized close to what I’m at, I added some minimal tension to HS, but far from questionable in terms of added airgun stress and mostly because ATM it was easier to turn HS little up instead of digging the valve to close it up just for a few degrees.
I haven’t even tested air efficiency but roughly it’s not below 30, maybe even more.
I hope that this findings are helpful for you all, I would be very happy if I give you at least a small amount of knowledge that you all gave to me.
ATB
S.
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The problem with the U2 is the valve assembly is improperly engineered to handle the hard hammer strike that produces the best tune.
I'm now running a tune that shoots same 44gr slugs at 950fps but with a much lighter hammer strike. The tune now gives an ES of about 8FPS. All in all..., I am good with the tune as accuracy is still good and so far, the o-ring on the poppet has not split again after a few hundred shots.
I hope you have better luck with your 'hot' tune on your rifle than I have had with mine.
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