accuracy assitance

With my p12 scope down atm, a friend volunteered his to me to borrow and set up for this weekend. after getting the gun set up with this scope (bugbuster, almost wont fit on the rail to be shootable) i noticed after sighting in the gun started slinging lead to the left. odd since this gun likes throwing pellets to the right usually.

anyways, it will hit where its sighted in at once in a while and put up sub 1/2″ at 50Y but is very inconsistent. i tried using lubed pellets but thats didnt seem to work all that well and seemed to foul the barrel very fast.

i will try to get good groups from the gun tomorrow sometime but in the meantime why would it be shooting great then shoot off to the left? could my crown need attention? i havent tried shooting it without the shroud yet but should that be a step in my determining of what exactly is going on?

i also got ahold of a chrony from the same person till sunday. according to what i set it at without the chrony it was low 900’s (not bad for tuning by ear and eye) i have since turned it down to 890 and gotten about 20 extra shots per fill from this but accuracy seems to suffer from the lower fps as well.

any ideas?