I use whatever elk rifle I'll be using later in the season, so as a result I've used a variety from the 270 up through the 338 WM.

If just picking a rifle specifically for antelope I'd use my Kimber MT 243, or for good weather a wood stocked Kimber 84M 257 Rob.

Really, any cartridge will do from the 223 up.

“Perfection is Achieved Not When There Is Nothing More to Add, But When There Is Nothing Left to Take Away” Antoine de Saint-Exupery