Correct. The bore-ride nose on some designs (.30 cal, 6.5mm, etc.) actually have lube grooves to prevent the nose from leading the lands - or grooves for that matter, if they obturate that much. The softer the alloy, the shorter the bore-ride nose length you can leave bare, because the longer the unsupported column of lead, the more it will obturate, mostly at it's base. The lands will guide the nose, but the grooves offer no structural support.So are you saying that if that the exposed bore ride nose is soft enough to bump up to groove that I might have an issues with leading proceeding the patch which can tear up the patch?
Harder boolits OR shorter exposed nose length. Of course, this means seating them correspondingly deeper in the case. I have seen people generously anoint the nose with some smeareable soft lube and they seemed to meet with success, but it was also a one-at-a-time range exercise. Can't imagine slipping those in a bandolier and heading for the field.I guess if I have leading with these relatively soft bullets and some nose unwrapped then I can cast some harder bullets to see if it gets rid of the issue. If the issue is gone at that point it's probably from he hard alloy not being able to obturate.
That could be - there's a bozillion different mold designs out there. It makes sense to have a PP mold that also has a bore-ride nose intended to be patched to bore diameter, say, .441 or .442 for a .450 bore. Another option is to have a two-diameter Lyman type "in-out" sizing die cut with your particular bore dia. and throat dia. so a patched boolit could be inserted and brought to the needed finished diameters. First, though, do some shooting to find what works before investing in a custom tool.I've seen some swaged bullets with almost a SWC type shoulder and a reduced diameter shorter nose. I'm guessing it's to solve the issue I'm running into now.
I don't recall whether you said you were using smokeless or black. The .45-70 is a voluminous case and I suspect that satisfactory velocities with smokeless could be achieved even with the boolit patched halfway up the ogive and just seated deeper in the case. That's conjecture on my part - the veteran Sharps shooters could chime in here and correct me if I'm on thin ice regarding pressures with that idea. If you're using black, you'll need the case volume for propellant, and a bore-ride design with an appropriately patched nose becomes desirable.
I'm with OverMax on the jacketed vs. patched friction question. Copper readily transmits heat which may reduce heat transfer to the steel. Paper is a fair insulator as well as being not very slippery. The boolit obturates outward against the patch on firing (or is squeezed down by the throat, or both) and the texture of the paper is pressed into the lead while the paper presses with equal pressure against the barrel steel which remains smooth, hence, it's easier for the patch to stay with the boolit. The same thing can be observed when unwrapping a patched boolit which was patched at full diameter and then sized.
The patch will be shed immediately on exit from the muzzle and torn to a puff of confetti. Sometimes I find tattered strips a few feet out front. OverMax is quite right with saying the longer the patch stays on, the less accurate they'll be.