Barrels for A 5

  I am new to the sport. Just bought a new A-5 and was dissapointe at 30 yards. I shoot competitive archery and have a chrono. I set the gun at 280fps., I did not put anything up to shoot at. Just shooting at a tree in back yard. I tell you that there is no way you could expect to hit a person standing upright with any consistency! I have been reading on other sites that the Tippmann A-5 barrel must be the first to go. What I want to know is what kind? What length? I want accuracy at least to 60 yards. What does different length barrels do in terms of acurracy, speed and air or gas consumption? I am willing to buy a barrel, but was really dissapointed at how these balls nose dive at 30 yards. I would have to aim over your head to get a mid body shot.