“...I suppose a .68 would scare the pants of them.” [tet68, post 6]
I will confess a 68 would give me something of turn. Because there aren’t any, unless someone has commissioned a custom piece or two.
69 cal (0.690 inch nominal or diameter) was the official US caliber for standard-issue small arms from the beginning, until 1855. Before the beginning actually, when the French began selling used muskets in their national caliber (69) to the fledgling United States through false-front business entities and fake end-user organizations … by the time the Americans beat Gentleman Johnny at the two Battles of Saratoga, muskets of French pattern (chiefly the M1763 made by the French state arsenal at Charleville - hence the common name for them in America) were there in large numbers and became the preferred piece for US issue.
When the new nation set up arms manufactories at Springfield, Massachusetts and Harpers Ferry, Virginia, the very first products were smoothbore muskets of 69 cal, almost identical with the French muskets furnished earlier.
The first official US rifle was the M1803 built at Harpers Ferry. Soon, official rifle caliber was 54 (0.540 inch bore diameter); the dual-caliber arrangement (54 for rifles, 69 for muskets) persisted for decades, until the adoption of the M1855 Rifle-Musket in 58 caliber.
But the 69 cal arms did not vanish instant. Many thousands stand of arms had been stored away in armories; a great many originally flintlock had been converted to percussion. Some saw issue early in the American Civil War; some were rifled to take the 69 cal hollow-base bullet of minie pattern - a truly formidable projectile weighing some 730 grains made of soft lead.
A number of US rifles were reamed out from 54 cal to 58 cal, and re-rifled, to match the then-new rifle-muskets. Standardizing the ammunition helped.
Some muzzle-loading authorities declare the 0.680-inch diameter round ball to be the proper bullet for 69 cal smoothbore, but after a couple shots, there will be enough fouling to cause difficulty in seating that big a ball down on the charge. Original French loadings used a ball of 0.627 inch diameter, to facilitate loading even into a heavily fouled musket barrel. Charge of that period was 189 grains of black powder.
Some experimenters have obtained good results from modern replica 69 cal muskets using 0.662-inch diameter (nominal 16 gauge), loaded atop sleeved wads for 16-ga shotshells.
Back when I was heavily into black powder, I decided that .50 cal. was the best all around.
Round balls were fine for deer and anything smaller. You could use the heavy long bullets with beeswax in the grooves for heavy stuff.
I used mainly Pyrodex as some of the newer substitutes were not around back then.
I had a Sile .54 copy of the Sharps. It was the model using caps. It was really pretty, but not quite as well made as the ones made in Montanan. Mine was made in Italy. I could see no advantage of the .54 over the .50. Either one would do the job.
When I say “do the job”, I would never hunt dangerous game with a muzzle loader etc. without a modern backup.