Once again. You are perfect vertically. Your first group was 3 shots one inch right of center(maybe .75 right), and the second group is about 3.3 in. right of center, again perfect vertically. That's just a light breeze that came up between the first and second group, that you didn't know about. It really is the wind. I've seen it happen at ranges from 300 to 800 yards, and sometimes its so light that if you or your spotter aren't paying close attention, you won't know it has happened. And there's always wind. There's just no such thing as a perfectly still day. If you went out tomorrow and the wind was 3 mph right to left at 400yards, you'd be 3 inches left with the center of the group. If you were doing anything wrong in your shooting technique you wouldn't be shooting .5 moa at 400 yards. Also, spin drift would only account for about .7 or less inches at 400 yards. Its sufficiently minimal that it doesn't get calculated in for snipers in the military until shots are past the 700 meter range or farther, depending on barrel twist. Almost all other factors such as altitude, humidity, temperature etc. effect vertical placement and not horizontal impact. Someone here mentioned Coreolis force, which is earth rotation during flight time of the bullet. You might get 0.2 inches at 400 yards, which your group would mask. It isn't worth worrying about. I shoot with retired snipers, and am a retired advanced marksmanship instructor for the Army, and this is just caused by a slight wind. By the way, no deer, antelope or elk would notice that your shot placement was 2 to 3 inches right of point of aim. All your shots are going to hit vitals and kill your animal. Also, remember: perfect is the mortal enemy of good enough. You'll chase perfect forever and never see it.