Rangers have the highest accuracy in the game (marked for the hunt, accurate wounding shot, concussive tranq, various passives, etc.) so they can easily break the penetration barrier with crits.
I use a ranger/monk(wanderer) so in addition to crits, I also have the tenacious buff from monks, which adds 2 penetration (3 extra on crits due to the +50% pen bonus). This allows me to get 21 (11 base, 6.5~7 crit bonus, 3 tenacious buff) penetration on most of my hits.