Well, maybe I've just been using the wrong bullet.
I slugged my bore again tonight twice using bullets that had been sized to .542. Making the most careful measurements I could with my Mitutoyo digital calipers, this is what I believe I have for a bore in this Pedersoli 1859 Sharps:
When I tap the bullet through the bore with a .5" wooden dowel, it forms quite a wavy "skirt" around the base of the bullet, with the skirt being longer where the lands are.
The skirt is not uniform around the bullet, probably due to the dowel rod not being centered on the back side of the bullet when driving it through. I don't know if a similar effect happens when the bullet is propelled by a powder charge or not. I would expect full pressure to be uniformly applied to the base and so the effect should be uniform, if not less pronounced.
In any case, if there is lead extrusion behind the bullet it probably isn't good for accuracy.
I've been shooting the Eras Gone Sharps which measures .549", unsized, and also sized to 542". Unsized, this bullet is compressed .0235" in the lands, and .0115" in the grooves. Sized to .542", it is compressed .0195" in the lands, and .0045" in the grooves.
Conventional wisdom as I understand it is to use a bullet about .002" over groove diameter, so that means I should be shooting a bullet around .540".
I have had folks recommend to me "bore riding" Christmas Tree bullets, where the first driving band actually goes down the bore and the second driving band stops on the rifling. Moose Molds' 544-480 Christmas Tree has bands .520", .534", .544".
Steve
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