Airgun Technologies Uragan 3 177 600mm Tuning

[Jfk742]

Got a new rifle and it came to me doing 1029 fps, ~24.5fpe. I got it to hopefully shoot silhouettes and HFT so it needs to be >20fpe. I probably should have gotten a different gun but here we are. I’ve been reading a bit on tuning this type of rifle and have had some input on where to start with it by some helpful members. My initial testing has shown JSB exact 10.34 are really accurate and stable at 46yds. 10 shot groups at that distance were a touch over moa, using my fist as a rear bag, forgot my sandbag….

I started tuning today. My plan was to start by cranking the HS out 3 turns and the fps dropped a whole 7 fps on average. Next I pulled the valve and did 1/8 turn in, regassed to 250b and took another 1/2 turn out of the hammer spring, fps dropped down to 906fps. After a 10 shot string I had an es of 15. I put a 1/2 turn back in on the HS and the velocity shot up to the 940’s. I decided to get back into the valve and lower the setting a little more, though I started to turn the valve OUT (ccw) by accident then turned it in another 1/8 turn. After putting it all back together my fps went up to the high 960’s, I didn’t bother shooting more than a few shots and had to put it away for another day.

My initial impression is that I can get to >20fpe, with a stable enough shot string, es and sd, hopefully with no more than a little fiddling with the valve and HS. I was shooting at 12 yards and everything was going in the same hole but that’s really no indication of accuracy ime.

My plan is to get the speed down some more with the valve and then tune the HS tension over the course of a few days, letting the rifle sit between adjustments.

I have zero experience with a balanced valve and only slightly more with a Mrod from about a decade ago, I’m green to say the least. Any input is appreciated!

 

[greenbeans]

This is what the U3 is capable of in terms of ES/SD:

Not sure whether you can get that right with a very low reg setting but you should be able to get somewhat close. For that to happen you have to accept how a balanced valve works though, which means you can’t use the hammer to fine tune the speed. You want the valve to open fully every single time, everything else is not going to be this stable. To find the right hammer setting doing this for a given reg pressure, turn the adjuster out until it doesn’t open. You’ll hear it and note a significant drop in fps once that happens. Then turn the hammer adjuster back in a 1/4 turn at a time. Once speed doesn’t increase anymore you’re there, maybe give it another 1/8-1/4 turn beyond that point to be safe. That’s it. FPS are 100% controlled by reg pressure.

 

[Jfk742]

I tried turning it out until it wouldn’t fire but that only left me with 1.5 threads of engagement in the block, that was before adjusting the reg. As it came from Talon it was about flush with the block, maybe 1/4-1/2 turn out. I also saw a big dip in velocity (~100fps) with it turned way out, is that typical? I didn’t shoot it much like that though. With the HS a few turns out from flush it’s much more quiet, like 7-8db(using my buddies decibel meter) seems over gassed when the HS is flush. I should have some more time to play with it next week.

 

[greenbeans]

Yeah they come fairly overhammered as long as the setscrew is still grabbing the adjuster you’ll be fine but yeah, could be that the reg is so low that the hammer can’t be lowered “enough”….

100 fps is very normal once the valve doesn’t open fully anymore. Another half turn and you’ll be another 200fps lower and another and the valve won’t open at all.

 

[Jfk742]

Ok, reread your instructions and realized I misunderstood. I definitely found that drop off. With my initial reg adjustment I was in the 940’s after turning the HS in a 1/2 turn from the drop off in speed. I think I blew it on the next reg adjustment with turning the screw the wrong direction initially, given velocity increased a few fps. I had the regulator valve body, locking nut and adjustment screw all marked but sharpie almost immediately came off when I stuck the reg back into the gun. I may use a scribe next time so I don’t have to worry about marks being wiped off.

Another thought, would shrinking the plenum volume help with shortening the air impulse at the shot? I have a loose understanding of how the balancing works in regards to the valve, not sure if that idea is even viable.

 

[greenbeans]

No worries hmm reducing plenum might help you to get down further but you’d need a pretty robust insert that can withstand the forces at work. I’d try to play with reg a bit more first, seems like you’re almost there. Maybe another 1/8 of a turn or a tiny bit more will do already… but I know, uragans are amazing guns but a pain to tune… on the bright side, once they’re tuned they’ll hold the tune forever.