Fx Impact Problem

I’m a big airgun enthusiast and have been to EBR twice and very familiar with Airguns and have had many FX Airguns over the years I just picked up my FX Impact .25 around 7 months ago and love it it’s just absolutely amazing and have put a couple thousand rounds through it but just today has let me down when doing some general accuracy groups and had fired around 40 pellets and the very next pellet I load in I shoot and completely miss the paper at 80 Yards I loaded another and missed the paper again and was puzzled so I checked my pressure, and all of these pellets are from the same tin and I haven’t adjusted anything and load a new mag and try again at 50 Yards and find out my pellets are dropping about 3 feet at 50 Yards and I have no idea what is wrong, and all of these pellets are JSB MK2 what I have always used and the gun never made any strange sounds or anything, and for the record this is a gun I treat like gold I haven’t even so as bumped it it’s literally in perfect condition and I have been soft on it it’s whole life also I haven’t even adjusted my regular pressure or anything it’s stock just like from the box, and it isn’t the scope I have a Hawk with sports match rings My airgun shouldn’t be dropping randomly several feet something is wrong. Not a good day
 
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Thanks, and thinking back after this pellet dropping started to happen my pellets were very hard to load in the breech I had to really slide the leaver to get the pellet in the barrel I think it was my o ring coming out and getting caught in the pellet probe and also got my chronograph to work and I got a average of 806 FPS on max power on power wheel that’s really slow even for a 33.9 gain pellet. I just now edited this post because I have found a random o ring laying in my gun case under my Impact but I can’t figure out where it goes the breech o ring is in place