I bet it's the barrel length. But, I wonder if it's something else. You say you're barrels are over 2 inches? That means I have really long barrels. I'll try cutting an inch off. Also when i shoot the gun, without the turret, the're doesn't seem to be really much air coming out. Do you feel a blast of air come out when you fire yours? I took of the e-tape, but do you think replacing the o-ring would help?
How tight are the darts in the barrel? Could be a problem of matching foam to barrel material too.