There are books written on this subject so it is hard to give a brief summary for your question.

Different brands (companies) will sometimes shoot differently in any given gun, so you may have to try a few to find what your gun will shoot with some consistancy.

The BULLET loaded in a cartridge will shoot differently as well. And the weight and KIND of bullet (design) will have different effects on different game animals. Some bullets are light and fragile and will be good for shooting woodchucks and coyotes but very poor for shooting big deer. Some bullets are heavy and stout and are great for moose and elk but not so good for smaller deer.

Someone who uses a .270 will probably give you some specific loads that work well for them.

Robin down under