I have a couple Christiansen arms barrels I used for a 300 rum and 7-300wm. The first 2 shots from each are usually within an inch at 400yds, but the third flies off about 3 inches away. Shot off front rest and heavy rear bag on concrete bench. Shots are in succession then rest rifle for 10 minutes before next 3 shot group. Guessing heat is the issue. Thoughts?