why does this happen??

Hey guys. I was out shooting today at 50 and 90 yards getting some good groups after some setbacks I had with my wildcat. I shot around 15 magazines when all of a sudden the POI dropped about 4 inches at 90 yards. I clicked back to my 50 yard zero and the POI was low also. I clicked 3 moa to rezero and the POI dropped again a little. The groups opened up also. Why the sudden drop in velocity? I was still at 180 bar and there's no air leak. Any thoughts? Thank you. Eddie
 
"Mr.Gadgets"Your hammer spring screw may have backed off. Usually, I've heard, they are tough to turn, but my wildcat's was extremely loose (easy to turn).
This is possible.

What you should have done is topped back up with air and carried on. If POI rose up again you know there's an issue with the reg (potentially) or setup. If it stayed the same it should only be something in the hammer side causing the issue ie Spring tension backed off as above.
 
Hey Ernest. You probably realized this is the Eddie who's been emailing you about the issues with my wildcat. So I usually fill to 230 bar, shoot 5 mags (40shots) down to 150 bar. Then refill. I think my reg drops off at 140. When this happened it was still at 180 bar. I shot 2 more mags down to 150 bar with the same problem. But then I filled up to 230, ran 8 shots over the chrony and it was back to normal around 810. I then went out back and shot 3 mags and they were normal, good groups at 65 yards. Then I shot the last mag over the chrony down to 150 bar and was still around 810 average. It seems my regulator had a " hiccup" for some reason. Has anyone experienced this? Or is this a sign of a problems to come? Thanks everyone. Eddie
 
Hey hsnmz. Yes, adjusting the pellet probe, and drilling out the airstripper a little fixed the pellet spiral issue. So far so good. My groups at 90 were really good with no spiraling. I removed the grub screw holding the barrel in place and spun it 180º so I could see the barrel transfer port is lined up with the hole. Then I marked the pellet probe with a sharpie. I made a mark on the top showing where the rear of the air hole is and pushed the cocking lever forward pushing the probe into the breech making sure the mark lined up with the rear of the transfer port. Even being a millimeter or two to much forward will crush the skirt of the mk2's