the stuff i used was 7/16's thick and i could use it for all the tests. as said, i thought it would be like a rib or leg bone.i've shot 9 of these into combinations of catalogs gallon jugs, magazines and plywood. they're very similar to a berger and the Sierra might be just a bit tougher.
GG is going to test the 280's against the 300SMK's. my guess is the 300 will penitrate a bit farther.
as a foot note, i chrono'd one of these, it was 2770. my goal was to start them out as slow as possible to simulate distance hits.