Inner Barrel

Length and inner diameter both matter: a longer barrel lets compressed air act on the BB longer for more consistent velocity, up to a point of diminishing returns, while a tighter bore (tightbore) reduces the air gap around the BB that would otherwise let it wobble.

Barrel material, internal polish and bore consistency along its length all affect shot-to-shot spread, which is why aftermarket barrels are graded and sold by precision tier rather than just length. A worn or dirty barrel is one of the first things checked when accuracy degrades, well before assuming a bucking or hop-up problem.

Cleaning a barrel properly means running a cleaning rod and cloth straight through rather than back and forth, since dragging debris back across a scratch it just passed can deepen exactly the kind of imperfection that hurts accuracy.