Listen to ThunderCactus and CDN_Stalker on this one. They know the sniping game well.
Try a firefly bucking!
As far as barrels go, length can affect your shot. But as to how long versus FPS, rounds, etc has been a very difficult point of contention between airsofters. The most all around stable barrel you can get is the 6.04. If you want to increas your grouping a little, try a 6.03 but go no tighter. After that, you are very realistically only increasing FPS and BB destabilization. Some guns will use a 6.01 well, but I haven't seem many. For a longer range/accuracy, stay between 6.04/6.03.
ďREALITY IS LIKE A STONE. TO MANY ITíS HARD AND COLD, THEY CANíT HUG IT OR EAT IT, IT ONLY FRUSTERATES THEM AND DOESNíT DO THEM MUCH GOOD. TO OTHERS ITíS STRONG AND DEPENDABLE, YOU CAN BUILD WITH IT, BUILD UPON IT, OR WORK WITH IT, ALSO USE IT TO SMASH PEOPLE IN THE FACE.Ē