Klondiker, that 51 sure is in nice condition for that age.
I shoot Frontiersman category in cowboy action about 6 times a year at the big matches and at a few monthly fun matches. I switch hit back and forth between a pair of Uberti Remington NMA 58's and a pair of older Uberti and Navy Arms (still Uberti as I understand it) Colt 1860's. And once I do a touch more work to fix an issue with the nipples I'll be adding an older Navy Arms clone 51. All in .44.
Because I'm limited for time I've settled on powder, ball and a two drops worth of Canola oil onto the joint between ball and chamber wall along with a drop on the cylinder axle or arbor, depending on which set I'm using, to free up the fouling of the cylinder. I've never tried the bore butter but I know that while inky/greasy at the end of the day due to the oil and fouling the cylinders keep spinning very freely. And the fouling in the barrel is oily and wipes out easily. I seem to run into less trouble keeping the cylinder moving than those I see using bore butter. But I know a lot swear by it so YMMV. I just find it easier and less messy to use the Canola oil. As a bullet lube it works well. If I do have any lead flakes in the fouling and oil in the bore it washes out easily just with the bristle brush and there's seldom any specs of lead on any of the patches. I tend to not use bronze brushes unless I need it. I don't recall the last time in any of the four that I actually needed the bronze brush to remove any lead. I probably have but it's rare.
Accuracy does not suffer from this "shortcut" method either. When I do any target practice I find I can get groupings as good as I get with modern guns. So good enough that it's me which is the limit. I won't win any bullseye competitions any time soon but I normally do fairly decently. Like on a good day I'll get 3" groups at 20 yards out. Bad day maybe more like 4".