A few years back, I ordered a Lyman 457193 mould to cast some 405 gr bullets for my Ruger #3 in 45/70. The rifling that Ruger was using in that gun at that time was similar to Marlin's Micro-Groove rifling, and dictated that the bullets be oversized just like the 1895 Marlins in that caliber. The problem was that my bullets fell from the mould at .457-.458, depending on alloy.
I returned it to Lyman, but they sent it back as "within spec.". I had read in an old issue of the Fouling Shot that you could enlarge undersized bullets with teflon tape. I first tumble lubed the bullets with Lee Alox, and then wrapped the bullets with plumbers teflon tape that you can buy most anywhere. It took a little experimentation to get the right thickness, but surprisingly I found that I could achieve virtually the same accuracy and velocities as I could with Jacketed bullets.
Later I tried skipping the Alox step, and sized and lubed the wrapped bullet in a .459 sizing die. These were cleaner without the tumble lube on the nose, and shot just as well. This process is slower than molasses, but if you need a few rounds for hunting, etc., it will solve the undersized bullet problem.
