I have a 257wby Mag and I run it a little warm. I primarily shoot light bullets for speed. 75 grn V-Max, 87 grn, & 85 grn Noslers. Now hear is my question. Which solvent should I use for copper. I currently use Sweets 7.62 & JB Bore cleaner. The gun still has the factory Barrel and yes you can see machine marks on it when it is finely clean. Cleaning the copper out is a real chore and takes hours to do. I know part of the problem is running over 4k on some loads. I would love to take the Mark V apart and put a new barrel on but it groups under 1/4 MOA @ 4150 Fps. Thank you for your replies.