I bought a Remington 338 RUM, stainless / laminate w/ Swarovski scope at a gun show a few years ago. Came with a break that did not tame recoil much, so I put mercury in the buttstock - that helped. I found a better break at:
www.ccmuzzlebreaks.com

I have these breaks on several rifles and they work very well. The Remington is jus plain heavy, in comparison to my Browning A-Bolts and I'm wondering if the mercury insert removed would take much weight off, and, what else can I do to make it lighter to carry hunting.

Cut the buttstock to a length so it fits in the pocket of your shoulder while shooting (standing position) with hunting clothes on. Most stocks are just too long for me and pretty painful with anything of .30-06 or more unless I cut them to the proper length of pull. With the right length both my 375 H&H and 300 Weatherby magnum are no problem at all without recoil brakes.

Replace the stock to lighten it.

The only 338 RUM I have handled and shot was also heavy. I can't imagine it would be much fun to shoot if it was lighter.