All paintball are technically 0.68 calibre...every box or batch Will vary slightly ranging on average between 0.685-0.693
Mostly people Will simply either run a 0.693 barrel as its the std that comes with factory guns! , or Will have a barrel kit or selection to match as closely as possible to each new box!
almost impossible to.say really!!!!
so safety says get a barrel they Will Definately fit down!!