Although the above posts are true to a point they are not technically correct, a boomstick may be more efficient & accurate if by luck you buy the right back for the paintballs you are using.
A boomstick is two sections
Back - size printed on it
Front - length is preference to where on the field you like to play normally
If correctly sized it will improve accuracy but do not be fooled its not going to become a ball on ball sniper rifle, there are many variants that affect velocity, check out the thread "a gun that shoots more accurately" to see them.