Cylinder

As the piston is driven forward, air trapped ahead of it inside the cylinder is compressed and forced through a port near the front into the inner barrel behind the BB. Cylinder types are classified by how much of that stroke is ported — full, partial or bored — matched to a range of barrel lengths for the most efficient compression.

Mismatching cylinder type to barrel length wastes compressed air or starves the shot of pressure, so cylinder selection is a core part of any internals rebuild rather than an afterthought. A worn cylinder head or O-ring here is also one of the more common sources of an air seal leak.

Manufacturers publish cylinder-type-to-barrel-length charts precisely because getting this wrong is such a common upgrade mistake — worth checking against the chart before ordering a replacement cylinder for a non-standard barrel length.