1869 Sharps Conversion 50-70

[Blackpowder Burn]

Back to a topic from last year.  I've dug out the Sharps conversion carbine that I semi-permanently acquired last year and slugged the bore.  As the barrel was relined and has 3-groove rifling, I can't get an exact bore diameter, but did get the following information.

I measured across one land and one groove.  Assuming grooves are approx 0.005", I guesstimate the bore diameter to be:
Driving bullet completely through bore = 0.512
Driving just into the barrel at muzzle end = 0.516

There appear to be areas of different diameter down the length of the bore, as shown by the data above and the force to drive the slug varies quite a bit in several areas.  The bore has light pitting, but is actually quite clean with strong rifling.

I've never been able to get any sort of accuracy out of the rifle, even though I tried bullets from 0.512 to 0.515 diameter.  I had a recommendation early on to try a hollow base bullet to help deal with the situation.  The Lakota 378C mold (325 grain) was recommended.

Do any of you have any opinions, ideas, etc on the use of the hollow base mold or any other options?

[Trailrider]

A hollow base, relatively soft (1:20 tin:lead) backed by black powder might help accuracy.  The nominal groove diameter should be .515", but that could vary considerably.  I don't know if you've tried it, but a relatively hard bullet, Lyman #2 or equivalent (wheelweights + 50:50 lead:tin bar solder or linotype & 50:50 bar solder...see the Lyman manual for mixture proportions.  Modern wheelweights may vary in content from my 30 year-old ones!) may work. The Lyman #515141 sized to .515 or shot as-cast should help.

[JimBob]

Modern wheelweights may vary in content from my 30 year-old ones!) may work.

A word about newer wheelweights.They are increasingly composed of mostly zinc because of EPA regulations on lead.Bad news if you get it in the pot and try to cast bullets.When your melting them keep pot around 650 degrees.Zinc melts at aprox. 787 degrees and if the weights are zinc they'll float on top of the melt where you can remove them.