Which 7mag bullet

[Jack]

The difference in wind drift at 300 yards between a 140 and a 160 isn't going to be enough to worry about, in real world terms.
For the bullet you want, I might take a look at Speer's 160. I think they make both flat base and BT's - frankly, BT doesn't mean much at the ranges you're using it, so I'd probably go with the flat base.
Hornady's 154 would be another possibility.
Can't recall if Nosler makes a BT in 160, but, I might stay away from it.
I think the Ballistic Tip is a terrific deer bullet in a standard velocity cartridge. Not so sure about under 100 yard shots out of a magnum, tho.