I have a 7mm Rem. Mag. and a 7mm Ultra Mag. While I haven't shot my ultra mag yet, I have used the 140 grain AND 160 grain Nosler Partitions on whitetail deer and I don't see a difference. Granted, shots are about 100 yards and whitetail are thinned-skinned animals, but I would think that there might be a difference, but I see none.
Mule deer are classified as thinned skinned game, but are nonetheless generally bigger than whitetails. I have never hunted mule deer, but, from what I have been told, and from what common sense tells me, a heavier bullet would be appropriate. This is not to say, however, that a 140 grain bullet wouldn't work, because I'm sure it would.
I personally like to use Barnes X bullets. They are very accurate in my guns and weight retention is about 100%. I also like the "X" expansion they make. They may be a bit too much for whitetail and mule deer, but if you drop down in weight, they would be perfect. As such, rather than shooting a 160 partition, you could get a 140 Barnes X - BT (Boat Tail) and get super performance.
Of course the most important thing is shoot what's most accurate in your gun. Either way, a 140 or 160 premium bullet from your gun won't make much of a difference. :wink:
Just make sure that you use premium bullets because the super high velocity of the Weatherby simply demands the use of them over the conventional bullets.
Zachary
