Try several brands and see which one your gun likes best! I'm assuming you are talking about the 7MM RM. All 7MM mags are accurate, long range calibers. You are asking a lot for one bullet, but it can be done though! Bullets designed to penetrate and expand at 300 yds. might not work well at 20 yds. For the best results on deer size gamein a 7MM mag, I'd stay with lighter bullets from 139-150 gr.
With that said, I've just aboutretired my7MM RM for most deer hunting! Out to 300 yds.my .243 will do all that the magnums will do, and do it cheaper, with light recoilto boot!