Hmm I suppose the rear sight thing is one possibility, though I don't reall think that's the case. I clean my gun after every game, and after every couple target practices. I use the cleaning rod it came with and a tissue put through the top of the cleaning rod. I always keep my gun clean though, so I don't think that's the issue. And it's not curving to the left, it's actually shooting straight, just off to the left a bit. I've checked the inner and outer barrels...they seem to be perfectly straight. Could be the hop up chamber-misalignment thing. Oh also I'm using .20g BBs.
@ Schwer_Punkt_91 You said something about the outter barrel not being 'seated correctly'? If that were the issue, how would I fix that? Also how would I fix it if the hop-up nub was off-center? Just exploring some possibilities. Thanks for the help!