Caliber not as important as bullet. Both ends of the spectrum. .223 FMJ in the ear hole puts them down in their tracks. 400 grn. hard cast .45-70 punches clean through the armor, both sides. Excellent choice and my personal favorite. I've seen large boar shields stop .270 ballistic tips like they were BBs many times. Most soft points will come apartat impact on leg bones or ribs after they have mushroomed going through the shield, possibly deflecting and not doing sufficient damage to put the hog down. We have one old 6mm shooting those long round nosed bulletsthat penetrates everytime. We have recovered lots of bullets for comparison, remarkably even one .458 stopped by a big hog. Core-locks, bonded, hard-casts, solids, and penetrators are our favorites.