I use Silva-Brite 100 solder. Its basically one of the old pewter formulas.
But its harder to pour, needing more heat than lead/tin alloys like 50-50 but maintains it color better.
I always heat the barrel, because in pouring 1874 Sharps tips with the staff and ball not doing so simply results in a incomplete fill.
But these are more complex, if done so they will stay on the gun, than a tip like this
Dan