The easiest, and a mighty good one it is at 25 yards or so, is a .490 RB run through a Lee pushthrough sizer. My sizer sheared little rings until I readiused the entry edges, but that needed doing anywayand the resultant slugs shot well, minute of squirrel head at 25 yards. For best results lube before and after.
I have a 255 grain RF mould intended for the older .45 LCs that drops bullets at .456. It almost worked as a .45-70 plinker. I keep meaning to pick up some metal tape and shim it to cast a bit bigger and see how that works.
What did not work at all for me was the use of muzzleloader sabots to shoot .38 bullets. It might work for someone else if they were willing to put in more than the very minimal effort that I did.
On the thread that started me off on this, there was the comment that Lee moulds warp after 500 castings. I don't doubt the poster's sincerity. He was apparently casting of pure lead and at a much higher temperature than I use. I have Lee moulds in perfect condition that have cast several thousand bullets with tin enriched wheelweights at moderate temperatures.
Given the minimal cost of Lee moulds, it would be very possible to create a plinker mould by lapping a .45 pistol mould out to the desired size. I have lapped several out by .002 and have been happy with the results. .005 may be possible and you'd only be out about $15 if it did not work.
