80 or 100 percent gas cylinders

Hey guys, I’m just wondering if somebody can explain to me the difference between a 100 percent and an 80 percent air cylinder

U know how some have holes on the side yah?
Deoending on where the holes are, it dictates how much of the cylinder volume is actually used for compression, in a nut shell.

Basicly the piston will not start having compression until after it go pass the hole on a compression stroke, and where the hole (and I think size) is determine how many % of cylinder volume is effective