"That's just a goofy gimmick that couldn't possibly work!" was my ignorant opinion... until I tried it. Darned if it didn't shrink the groups from my .308 Kimber Montana almost in half.
It's only 20 bucks, so give it a whirl. Buy it from Cabela's and you can always return it if it doesn't help.
.......Aaaahhhhhh..... Another satisfied Kimber owner who is usinng it...