I have killed nearly a dozen pigs with a stag arms model 7 AR, a 6.8 mm SPC with a 20 inch barrel. I think 16 inch barrel is fine as the 4 inches difference is probably less than 75 FPS.
I think you might like the AR15 platform better (.223, 6.8 SPC, 6.5 grendal) since once you load up the...