I've shot a butt load of MB's through mine...work fine. BBBastards too.
For balanced accuracy/range I use 0.28's...and that's what I shoot out of my AEGs as well and that's just convenient.
I've found 0.30's to be a bit too slow for fast target shooting...fine for CQB/field use though.
Some places (e.g. TTAC3) require that you use 0.20g BBs for CQB. That's a good thing, since at those ranges it doesn't really matter and at those ranges there's zero benefit in upping the pain levels one iota.