I bought a new Browning X-Bolt in 7mm Mag. I shoot 160 grain Federal Premium Nosler Partitions. As I've been going to the range, I've been noticing that I start off grouping all of my shots into 1"-2" groupings, and then out of no where, everything starts shooting high. I've heard this could be due to my barrel over heating. But I never let it get too hot. When I notice it getting hot, I let it cool down. This only happens after about 6 rounds. My first 6 are usually within an 1" or 2" of the bulls eye, and then they all start shooting high. The groupings remain very close, they just shift up. Like, 4"-6" up. I've tried different stances, really focusing in on my breathing, and adjusting my scope. Could it be that my barrel is getting that dirty after only a few rounds? I clean it after every time I go to the range. I'm at a loss. This is only the second rifle I've ever owned and shoot on a regular basis. My other rifle is a Marlin 30-30 which I've used for deer hunting for the last 15 years. I've never had anything like this happen with my 30-30. If anyone can help shed some light on this, it would be much appreciated! Trying to ensure all my groupings with my new X-Bolt stay consistent before I leave for an Elk hunt in 10 days! I can't seem to fix this problem.