The 6.03mm won't cause any more jams than with looser bore barrels, given that you use high quality BB's and maintain the barrel well.
Don't simply cut off the end of the barrel. It's ridiculously hard to get a clean, clear cut on the end, and the crown would be virtually gone. This results in possible obstructions at the end of the barrel, and can contribute to pressure loss. Also do not bring FPS into the game with tightbores, as the change is miniscule. You should be aiming for tighter groupings when you get a tightbore.