Again...old thread for me but figured I'd add my 2 cents. I have 3 mossberg 500's 2 of them with cantilever slug barrels...one in 20Ga (9 Years)and the other in 12Ga.(2 years) I prefer my 20 ga all day long but the 12 ga is a serious brush buster and has its place. (usually in the hands of a buddy)
12ga is not as accurate as the 20ga. I find the remington 2 3/4 accutip are acceptable shooting 3 inch groups at 100. The winchester 3 inch XP3 shoot slightly better groups but are uncomfortable to shoot. Mine did not like the hornady sst. I tried about 6-7 different loads. I will try the lightfields, win partition and copper solids in the next couple weeks since the season is done and I'm bored. There has to be a better load than 3 inches at 100.
20ga is a tack driver with the Hornady SST shooting consistent 1-1.5 at 100. Flatter.I only tried 2 other 20 ga loads and neither came close so I stopped trying.I have mine sighted at 150 and have taken several deer at 150+ with my best being a large 6 point at 178 yards. He dropped without taking a step. I feel its easily good to 200 yards with nice my 3-9X 40
BOTH calibers and loads drop deer in their tracks. I prefer the 20 though...not as much damage, flatter with better accuracy and range, and just as effective. Largest deer in my life (235# dressed)was with the 20ga from 60 yards and he crumpled.