Velocity has a lot to do with penetration although people think a heavy arrow will penetrate more, arrows can be too heavy and detrimental to penetration . I like 9 to 10 grains and I don't like over 10 gpp although my wood arrows are. Ive shot a lot of animals and I hardly ever get a pass through , complete penetration almost always but pass throughs hardly ever, even when I shot over 60 #s and 650 gain arrows . Either someone is mixed up about their terminology or there is some bs on here with all the pass throughs with 40# bows.