I have not found greases and oils to give the best accuracy.
For target shooting I now use a "dry" patch. Something in the range of 5:1 water to Ballistol. Soak the patch material. Wring it. Let dry. Cut at the muzzle. Wipe between shot with a slightly damp patch.
That change has halved my average group size. Using that routine, if a barrel will not not shoot around 1" @ 50 yds with peep sights, something is wrong. With the old TC barrel I would be looking at 0.015'-18 patches and the 490 ball. Get a guided metal range rod and quality guided short starter.
Scota, that all sounds good to me, and most is identical to my own experience. I've been trying thread cutting oil mixed with water, but found that this lubricant used in mechanics shops obviously is great for attracting mould growth.
I come from the land of Ballistol...this old-timey gun oil is known for its antiseptic qualities. I will give your recipe a try.
10 years or so ago, I used to be soaking my patches in "Wonder lube" (US made, yellow, smelling like good ole Double Bubble chewing gum). Melted this stuff in a can on top of my candle lantern, soaked those patches, let tem dry - perfect patches in any kind of weather. When shooting in real hot weather, I used wads made from beer coasters, or some semolina, to protect my powder charge (Swiss grade 2) from the grease sweating.
When the Wonder stuff became harder to come by in Germany a few years ago, I switched to soaking my patches in (alcohol based) car window cleanser, shortly before loading. This stuff also works fine for wetting cleaning patches I run between shots. All fine but this method also calls for using those protective wads, or semolina, over my loads of grade 2 Swiss BP. I shoot poured charges of 46 grains for .395 RB from my .40 cal x 30" GM barrel, and 58 grains for my .50 cal flintlock rifles (one TC Hawken, the other with a .50 cal x 30 GM barrel, loading .490 RB, with 015 patches in all of the above.
It's been nearly 30 years since we been shooting BP rifle at distances longer than 50 meters (which is standard for competitions in Germany) ...at US military bases, in Wiesbaden, Grafenwoehr, Kaiserslautern, Wildflecken, all in Germany. Found that 100 meters plus distances appear to be hard on a RB, with only some lucky shots. At those 100 meter competitions also popular in Germany you don't see any round balls, competitors there are using cast lead projectiles, long cylinder with many grease grooves.