Double check to make sure the barrel and inner barrel ave been installed right, the hop-up bucking isn't causing the barrel to be slightly tweaked to one side, clean the barrel, check to make sure the muzzle of the gun is free of debris.
If all else, fails, change BBs and see if that makes a difference. I'd say new manufacturer or weight. Also, inspect your BBs to make sure you didn't get a bad batch by chance.
hold the gun steadier
I'd suggest this as well if everything above fails
Chrono, that was brilliant by far. Oh, and OP... I just noticed you said you used some duct tape for something... make sure that isn't causing your barrel to be a little not-so-straight.