My very first brand new rifle was a 7mm08 that my dad built for me. It was for my 12th birthday so it was in 1979. It was a graduation up from my .243 which had been one of dads little trainer guns and still is to this very day. That little .243 was in all his kids hands and was the first rifle other than a .22 that my twins shot. Obviously my 7mm08 was a wildcat rifle as that was well before Remington adopted the cartridge as their own little invention. Even though the old man and many others had been using it for years. 400 yards, depending on your abilities, is within the range of the 7mm08 with the proper bullet weight. I wouldn't drop below a 139 grain bullet if you plan on reaching out there. Also, as younggun308 suggested, you will want to kind of split the difference on bullet toughness. You will want a bullet that will hold together well at close range and still open if you do have a situation where you have to really reach out. Our family has become real Hornady bullet fans over the years. I have taken a ton of deer and elk with the interlock line. They perform well at close and long ranges where the bullet has slowed a good bit. But my old man did have a saying and I tend to completely agree with it. Just because the rifle is capable of that range, doesn't mean you are. 400 yards is a pretty good reach for the common individual. Near twice as long as most ranges have for practicing. So if you do plan on that shot, please don't think you can use some ballistics calculator and holdover. Practice a lot so you can have the confidence and ability to put that bullet in the spot that will bring that animal down quickly.