I use Koppers all weather lube, Shooters Choice, Tetra Gun Fluoropolymer penetrating heavy-duty grease lubricant, or RIG Grease.
Tetra Gun may be the "slickest", but I do not think it matters as long as you use Grease and keep your rifle "
Greased Up." I have a couple of thousand rounds through each of my doubles with no apparent wear. I do not spare the grease.