I recently got an NEF Handi Rifle cal. 45-70. Way back, I had a Marlin 1895 which I got rid of due to recoil, and because it can't shoot as far as I can see- which is a ways out here (I was young then). So I plan to use cast boolits mostly, and try to come up with a round nose hollow point gas check soft lead load about 400 grs.boolit/ @ about1400 fps. which will expand reliably. I've researched a little, and found several loads that are supposed to achieve 1400 fps. while producing around 15000 CUPs with a 400 grainer.
First off, I did a chamber cast. No freebore, no leade. Case ends, rifling begins. I can see that with a repeating rifle this might be one way of doing it (what with operating length), but it still wouldn't be the best even there, especially with a .486 chamber neck area. What keeps the boolit straight on, and concentric as it engraves? (nada) So the first question becomes "how much throat/ freebore"? About an hour later I ordered a throating reamer from Brownell's (.460 throat, 2 degree included angle).
I'm somewhat obsessed right now with keeping the boolit straight on as it begins it's journey, and supporting the (soft) boolit against obturation as ignition occurs, and it transitions into the rifling. Would seating the bullets just barely (don't read too much into this) into the cases, and letting them jump .100" or .200" into the leade whilst contained in a freebore the same length as the cylindrical portion of the boolit work? It looks to me as if- what with the soft lead, a boolit with a short nose, goodly length bearing area, and fired with a low pressure load it might just do. Plus if we set it up for 300 grain boolits with a .500" long freebore, it might work well for 400 grainers (maybe 500 grs. )too?
Your ideas and advice will be appreciated. Ted