i want to know at what distance does a paintball start drifting down? if set at 300 ft per second?

Snipping in paintball is not the best idea considering the round ball and the imperfections in the ball cause every shot to vary. The barrels that advertise rifling dont really affect anything.

But using any marker that is shooting at 300 ft/s will be accurate at a max of 100 ft. You could lob a ball and pray at over 150 ft.

You can use this link to find more accurate information as far as gear goes