Several years ago, I saw a tool for lubing 58 minnie balls. It was plastic and screwed on a TC Bore Butter tube. The minnie was pushed thru the hole, while lube was supplied by squeezing the tube. It worked sorta like the Lee push thru sizing die that screws into a reloading press.
The grease grooves were filled using this tool.
I fill the base of my Lyman 577611 minnie with Bore Butter by hand and also the grease grooves. They shoot OK, but found the second shot impacts a few inches lower at 100 yards, with a dirty barrel. If the barrel is cleaned between shots, they all hit in the "same spot" or close.
Hunting elk with it for years and only got the second shot once.
I load a card wad over the powder, then a lubed felt wad, then lubed minnie, then another card wad. Without the card wad, the minnie tends to work toward the muzzle when trail carrying. November elk in Oregon Cascade Mtns tends to get your powder damp. Electrician tape over the muzzle helps keep out the weather (rain, fog and snow).
Rifle= Navy Arms Hawkin Hunter with slug barrel, stout load of 3F powder, musket cap and the Lyman 577611 home cast minnie. Peep sights as no scopes allowed here.
75 yard shot on cow elk.
Dave