Wildcat power drop?

[GA_LeadHead]

After talking up my WC MK3 BT on some other posts today, I thought I would get it out and do some shooting. Noticed a 20fps drop in velocity. Same tune I've always used. My "magic tune" for hades pellets. Same tune, same hammer weight, same hammer tension screw adjustment, same power wheel setting. 20 fps slower.
I took the hammer weight, spring, etc out and inspected. All checked out.
Shooting consistent and accurate, but a 20 fps drop.
Anybody know what could be causing this?

 

[scubajeeper]

Are you shooting from the same tin?

 

[cmatera]

Your cocking lever may have slipped a little on the valve rod.

 

[Headshots]

Is there a big temperature change from indoor to outdoor ? I have read articles about loosing fps in the colder months. Some say 10 fps for every 10 degree decrease. They blame lubes thickening, and slower moving regs or valves in colder weather conditions. And running their peak fps in the warmer months.

 

[GA_LeadHead]

Your cocking lever may have slipped a little on the valve rod.

Didn't think of that. I'll look into it. Thanks!

 

[GA_LeadHead]

Are you shooting from the same tin?

Definitely not. I go through a couple of tins if not more a week.

 

[tor47]

Did you measure on the same light condition with your chrony? Also some chronys can read a litle different if you do not shoot in a straight line trough the center of it. If the gun is new it might have broken in some, like the reg has increased a few bar. I would not worry to much about, as long as it shoot consistent. 20 fps is not much. My vulcan 2 to can have velocity spikes of 30-40 fps, within 10 shots on the bench, that is a bigger problem.

 

[GA_LeadHead]

Did you measure on the same light condition with your chrony? Also some chronys can read a litle different if you do not shoot in a straight line trough the center of it. If the gun is new it might have broken in some, like the reg has increased a few bar. I would not worry to much about, as long as it shoot consistent. 20 fps is not much. My vulcan 2 to can have velocity spikes of 30-40 fps, within 10 shots on the bench, that is a bigger problem.

Using a LabRadar (doppler radar), not a chronograph. Had the gun for a year. Was shooting fine until today. This rifle has not fluctuated 20fps ever. The tune I'm using had a standard deviation 2.7 fps. I could switch calibers, or ammo, come back to this tune, and the lab radar would show it true give or take 3-5fps at the most every single time. I shoot a LOT. Tin or two a week at minimum.

 

[tor47]

Maybe breach O-ring start to wear, small amount of air escaping?

 

[R0B]

Hammer spring weakening?

 

[GA_LeadHead]

Maybe breach O-ring start to wear, small amount of air escaping?

I was wondering if that was my culprit. I checked if the cocking lever and it had not slipped. I tried a new spring. That didn't fix it.
I'm leaning towards replacing the breach o-ring now because if I put my 25 cal barrel on or my 600mm 22 barrel, their tunes still show the velocities I expect from my tune "recipes". It's only my 500mm 22 barrel that has the drop in velocity.

 

[GA_LeadHead]

It was the breech o-ring. Replaced it this afternoon and instantly the fps was right back where it should be. Thanks for all the suggestions.