Re: 300 Weatherby Mag
I don't understand trying to turn a wby300 into a varmint gun. There are better platforms for that. A 150 is too small for large game and a Wby300 is (IMO) to large, or at least overkill for whitetails. Hell, my brother has probably killed more than the average hunter will ever see with a 30-30 I gave him 20 yrs ago. Unless you are hunting beanfields or powerlines you really don't need a big stick. Most of your shots are going to be well inside of 200 yds.
If I want to shoot 150s I'm going to use something that doesn't pound the crap out of me, like my 308, if I want to shoot elk and I've got a 300wby in the safe I'll grab it, but I'm probably gonna run a 180 or a 200. (I don't have one, I've got a 7mm RM, and I don't use it for whitetails either, I use a 308)
If he's dead set on running a 150 in the Wby I'd look for something that is going to hold up better at the velocity he's going to make. Just guessing but probably something like Hornady Interbond or GMX, or Nosler Accubonds or E-tips. I've got no experience with shooting these, but something like that may be worth a try.