Just the cheapest bullet you can find that is legal in your state. There's such a huge permanent wound channel with a high power rifle on such a small critter that even fmj would work great. Honestly not going to get much expansion (if any) with a deer bullet. With a varmint round, well if he wants to blow big holes in them just for kicks you could load him those up. Bulk pack rem core lokts would be my choice if they were cheapest. Haven't had to buy bullets in quite some time so I'm no longer up on the cheapest ones available.