I've built a couple of .416 Weatherby's. I've got a few questions for those in the know. My .416's have 1 in 12" twist barrels. These guns weigh about 15 lbs. When shooting 300-325 grain jacketed bullets above 2800 fps, my groups really start to open up. I've read and heard that alot of the guys with 416 Barretts are using 1 in 14" twist barrels for loads at 3100 fps and above. Do you think I have too much twist in the barrels at 1 in 12"? Another problem is that when I shoot the barrel warm ( meaning 3 shots or more) the jacketed bullet groups open up from .5 MOA/.75 MOA to 1 1/2 MOA. Cold bore groups, the gun is very accurate. Any amount of heat in the barrel and the groups open up significantly. Too much twist in the barrels? Are the 1 in 12" barrels better for the longer, heavier .416 bullets such as Cutting Edge? Or is it barrel harmonics/vibrations? Any thoughts?