12 gauge.If you want a good all purpose gun,i reccommend a Stoeger 2000 with a set of choke tubes.A good all purpose gun from any thing from squirrels to deer.I bought mine at Academy,walked out the door at about $530.Let me warn you with 3''magnum turkey loads,it kicks like a mule!The shell i use is high brass 6 shot.(2 3/4in will not be as bad as the 3'' mags). It will probabley kill a groundhog at bout 30,35 yards.