You could simply buy a stick of SPG or Lyman's Black Powder Gold bullet lube - it's cheap. Both are excellent black powder bullet lubes. I've used both of those with R.E.A.L. bullets when testing them in my .45 FlintLock and both worked very well - fill the grooves - you'll catch on quickly how to do it - wiping it into the groves with a finger, run the stick top of the bullet to the bottom to leave a chunk. The heat of your finger will then soften the lube so it can be 'wiped' into the grooves.
I was able to shoot 2, 5 shot groups with no wiping, then without wiping the bore first, easily load a .445" PURE lead ball with a .0225" denim patch for the 11th shot- which struck centre as it should. I had no problem using the rifle's 3/8" hickory rod, but of course, that load needed to be short started of course.