I use an RCBS kinetic bullet puller that has been modified and used as follows.
With a suitable tapered reamer or sandpaper (or emery cloth) on a tapered wooden dowel, open up the mouth of the bullet puller so that the case will go in until the rim can seat directly on the top of the puller. I used a large taper pin reamer, you want a very gradual taper not a steep angle. Do this by hand, not with a power drill, or else too much heat may be generated and possibly melt the plastic. Put the loaded round in the puller with a collet on top of the case rim and screw the cap down as usual. If you have various diameter collets be sure and use one where the hole is larger than the primer.
This system works for me for the 56-50, 50-70 and similar sized cartridges and the puller can still be used as normal.
HHW