I'm relatively new to reloading so I might be overlooking something simple. I developed a 300 win mag bolt gun successfully down to repeatable .25 moa groups as my first foray into reloading. Once I got that done, I started on a 308 ar10 I built with a rainier 18" ultramatch mod2 barrel. I have gotten a few loads to group down at around .25 at 100 yards, but each load I've developed has been wildly inconsistent when I test further. With the same exact recipe I've had swings as wide as .25 up to 3.1 moa. My 300 magnum never had this issue, and was very consistent with all the loads I tried during development, whether they were good or bad. I've looked the gun over thoroughly and don't see any obvious issues there. I've tried 2 different powders and 3 different projectiles. Im not a regular cleaner, but I gave it a deep clean to rule that out as a variable. All loads exhibit the same inconsistent swings. Right now I'm playing with neck tension but haven't seen any useful results from that yet. I'm hoping there's something obvious to a more experienced reloader that might steer me in the right direction. I'm starting to wonder if the barrel has some sort of manufacturing issue, or there's some weird harmonic problem going on with it. My goal for this gun is consistent 1/2 inch groups at 100, so the best groups have exceeded that, but the consistency problem is driving me up a wall. Any suggestions would be greatly appreciated.