56-50 bullet diameter

[John Morton]

Hi All, I want to purchase some "Soft Lead " bullets for my 1860 56-50 (3 groove relined) Spencer Carbine to reload. This gun is one that they relined after the skirmish from 52 cal to 50 cal. I slugged the barrel. Because the "Lands are not across from each other (3 groove) it is difficult to measure, but the widest I get on the slug is .510.
Can anyone recommend a bullet diameter? Does anyone have the same 1860 Carbine that was relined to".50" after the skirmish (1866-67) that they reload cartridges for? Thanks, John

[Herbert]

Roll the slug between a set of digital or dial calipers with slight pressure on the jaws,you will get a high a  low reading that will repeat as you roll the slug .the high reading will be very close to groove diameter,ad .02to this and you have the bullet size you need