On the rifle barrel? Can't say that I have heard of that. But I have put a Limb Saver Recoil Pad on my shotgun and I really like it. Better than any factory recoil pad the I have seen. I just don't see where one on the barrel would do you any good.
I've never tried it, and I can't imagine any real gain from it. Not for hunting anyway. Maybe if you're a high-power benchrest shooter it may clean up your groups?