Just to Add to what Pappa says, you also need to SIZE your minie balls after they are cast, to about .001" SMALLER than your bore diameter, so that there is only a minimum amount of obturation needed to fill the grooves with that base "skirt". A greased minie ball, properly sized, will slide easily down a CLEAN barrel, with just the weight of the steel ramrod assisting the travel.
Loading techniques vary, but some shooters like to lean on their ramrods to force that thin base "skirt" to expand on the powder once seated. Others just seat the bullet on the powder. Still others seat the bullet on the powder and then put a thin OverShot CARD on top of the bullet to keep it from moving in the barrel if the rifle is to be carried around for any length of time, before it is shot. ( a .58 caliber rifle would use a 24 gauge OS card, available from TOTW, Circle Fly,and other suppliers.)