Here's my thoughts on your situation.
I doubt than any material in "your" 300 WM will noticeably reduce the fouling.
If it fouls that much I'd recommend at least a partial Tubbs Final Finish process. Something like using 1/2 of each group of Tubbs bullets and not using the most course ones at all.
As far as the juice and velocity goes if friction goes down, pressure goes down, velocity goes down. If
this is the case then the juice is doing something. To return to original velocity an increase in powder charge would be necessary. (Has been know to start arguments
The stuff I tried required a barrel treatment after each shot. Not worth the effort.
Google on hBN for rifle barrels. I'm gonna try that next.