Pretty close. I use a 4 ft square box, 5 ft high made out of 2" lumber on 4 sides, the back with 3" bridge timbers. Fill it with ag lime, ground limestone. Never had anything make it halfway through, even 300 Mag and 338 TSX bullets. My 180 gr Saeco #315 clones at 2200-2450 fps out of a 308 goes as deep as the TSX out of the magnums.