Yes a micro groove Barrel @homebrew.357
i will run thru what i do with a new rifle to use cast in and maybe something will be of use to you .. . you probably know it already.
with a micro groove barrel especially bullets should be 1 or 2 thou at least over groove diameter, some molds your fcked before you start if theyre under sized.
your choice of alloy plays a part in bullet diameter.
mine go thru a .311 sizer when lubing, using gas checks.
choose the correct mold design for the 30/30 in lever actions.
personally i like a bullet that slightly engraves the rifling on closing the bolt or lever.
a light crimp for hunting bullets in tube mags . . .
i have used the 150grn. LEE .308 mold in the past but that was in my preMarlin days . . . the mold was good to use, cast good bullets and it went as well as any others in my Brno, same 1-10 twist.
longer heavier bullets are my first choice . . they dont work any better than shorter bullets but they just look right to me.
Yes to the filler with light loads . . which is something else to keep in mind, the amount of filler can be a factor in group size.
good news is using 7.0grns in my 30cal subsonic loads i get 1000 loads per pound of powder . . . with good accuracy . . but not for the sloppy reloader, a double charge things could get real ugly.
that black powder ( known as Holy Black to some ) will get peoples attention when it goes off . . . my first 45/70 was a Martini rebarreled with a Hawkins barrel that came with a swag of Black Powder ammo, liked firing the ammo but didnt like the mess/cleanup later . . . one of the worst guns i have owned with a terrable stock that smacked me in chops every time i fired it, a valueable lesson learned, stock design does matter.