Could be any number of things. Certainly letting the barrel cool between shots would improve things. Getting the bore clean should also help.
Most high-powered rifles have an accuracy preference for loads. One load will shoot poorly, another will be a tack driver. Based on your description, I didn't get the idea that you tried different loads. Before you do something drastic, try some different brands of ammo, bullet weights, etc. plus, slow down and let the barrel cool and do a good job of cleaning before you go out.