TAC 15i sighting issue
Hi guys, I am new to the forum and want to learn about my TAC 15i as much as I can to get it ready for the season. I bought it about a month ago and so far made about 70 shots. I've done all the fine tuning and installed Timney trigger and Countersniper Optics 2-16x44 with TDRM reticle. While installing the scope I figured that picatinny rail is not exactly level with the frame (far end of the rail is a little down). I compensated this by the front ring and and I've been making decent groups from 15 to 60 yards, but here is the problem: after a few precise shots, arrow starts hitting down (not right or left though) and I can't find any reasonable explanation why is this happening (yes, I shot the same arrow). I double checked - everything was tight and straight and I tried to be as consistent as possible from shot to shot. I put my TAC 15 aside for 10-15 minutes, then made a shot and it was perfect again. After 7-8 shots all of a sudden I hit well below again (5-6 inches at 30 yards). My guess is maybe it's some kind of a mechanical problem, such as release mechanism. Another question: both string silencers already need to be replaced. Is that normal after apprx 70-75 shots?
I will appreciate any assistance or comments as to why is this happening.