Screw that, you know the barrel diameter on most stock airsoft guns is actually 6.08 mm?
You're fine. If anything people with upgraded tightbores (6.04 and less) would be more likely to have problems.
Most BB's are 5.9xmm +/- some tolerance usually never going above 5.98.
Bastard's, Madbull, Airsoft Elite/Metal Tech, and BB King, all of them are good.
Don't use crappy BB's (like Walmart stuff but you probably knew that if you're wanting to get the "best" BB's available). I bought a bottle of crappy BB's cause I needed some for a game the next day and yeah.... chopped in my teammates PTW (it was like shooting confetti) and wouldn't even feed into mine (I would have to go full auto and maybe every 15th "blank" shot I fired would actually shoot a BB.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE