Re: 338 lapua woes.
My buddy got A sako TRG 338 and could not get it to group under 2.5 inches at 100 yards. After a few minutes of instruction on getting squared up behind the rifle he is now shooting moa to sub moa all day long. The 338 will really magnify any bad shooting habits you have. I would have an experienced shooter watch you while you are shooting ( the rifle should come straight back and not to the side, the energy should be transferred through your whole body and out your feet), I would also have someone load your rifle before you are going to shoot and occasionally not put a round in to check if you are anticipating recoil. If you are using good form, when you pull the trigger on an empty chamber the crosshair should not move at all! If it twitches at all your form needs work. If you are confident it is not you , the scope, the mounts, the ammo, there is only one thing left and that is the rifle. Send it to a good smith and have him check it out. I wish we were closer, I would love to give you a second opinion. My 338 is a 1/4 moa gun at 100 yards, I find it hard to believe that they settle down the further out you shoot (I am not saying it doesn't happen, I'm just skeptical.)
Good luck, and let us know what you find out!