The XLC's that Barnes made and were coated with molly reduced friction in the barrel and lowered the pressure as far as shoothing the same bullet without the coating. With the pressure reduced you could add some more powder into the case and get up to 200 fps more out of the round.
The only problem with them is that they don't make them anymore and if you like to shoot them and find any you had better buy all that the store has. I already have.
If you haven't settled on a load for your 300 WSM yet you might want to look at the Barnes Tipped TSX 168 GR Boat Tail bullet. I like to use one bullet and load recipe for each of my rifles regardless of what I am hunting. I worked a load up for my Kimber 8400 and that particular rifle REALLY like 63.5 grains of Win 760 underneath the aforementioned bullet. I took my cow elk with it this year and she dropped in her tracks. I read several articles about this bullet and it sounded really impressive and if my experience with the cow holds true for my bull, I will be using them in all my calibers. I did have to tweak the powder charge but once I found that magic number I have been more than satisfied with the accuracy of this load/rifle combination. I don't remember the exact numbers offhand but with a ballistic coefficient of .470, and a velocity of around 3000 fps, the point blank range of this load is way out there.
Anyone who shoots a sabot bullet has had the problem with loading the next round with a dirty barrel we have all struggled with it.
Between muzzleloader shots I have done some research and testing on my own to find out what works for me for the next shot. I have been using a product called bore butter and when the muzzleloader is just sitting around I leave it caked in the barrel for protection. Have also found that if I lube my sabots with bore butter they really slide nicely down the barrel....