Would a 156 or 160 gr .264 projecile bounce off a leg bone?

Hooey!

They have amazing penetration abilities.

PS I know a guy who culls 200 to 300 antelope in a week with a .243 (head and neck shots) and also uses the same rifle on eland.

Maybe he just shoots more than five rounds a year.

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If I was looking for an ideal calibre for gemsbok it definitely wouldn't be a .375 OR a 6.5x57. I think a decent flat shooting calibre such as a .300 Mag with 180 gr projectiles would be about ideal. I've never seen a wild gemsbok up close.