The difference is.....150s fly faster, recoil the leastand are good for up to deer sized game. 165s fly the flatest, recoil more and are good for slightly larger than deer. 180s recoil a bit more, slightly less flat than a 165, and are good for elk, moose, bear (might want a 220 for a really big bear). Now, the previous statements are made assuming we are talking standard bullets. Of course, one could expect a 165 grain premium bullet to out penetrate a standard 180 grain bullet.

Since the 30-06 is my hunting rifle, I have done extesnive research on bullets, powders and so on. I have decided to build a 180 grain load for everything that walks in North America. Enough metal to penetrate, flat enough trajectory to hit em, and light enough recoil as to allow me to shoot it very well.