There's an old Lyman #450229 in the fun box but no base plug.

Trying to figure out what to do with it...
I used the sprue plate to block off the nose pour hole and fill the mold from the bottom end with soft lead. Got it good and hot and saved four castings for measurement.
The three drive bands are .455". The plug channel is .445" diameter.
I've been tinkering with the idea of using it with an adjustable length hollow base or flat base plug to create a .445" diameter tail end that would drop into the .446"/.447" diameter chambers on Pietta 1858 Remington reproductions.

But I recomembered, around here somewhere there's an ancient box of those thin Ideal .45 gas checks and maybe they might be usable. Around here, somewhere...