MAIN TURRET:
Both Lancer and Driller can pierce zombies, but how Lancer crits is different now.
Driller:
Can pierce one zombie, hitting another behind it. Crits work as expected. The crit chance rolls per-zombie hit.
Lancer:
Can pierce all zombies in it's path. If the first zombie hit is a crit, all zombies in that shots path are also crits. (if not, no zombie in that shots path will crit).