Marty told me when using 10 mm Mag brass you need to dehorn the 6.8 SPC extractor, just rounding off the sharp corners. If you form from 6.8 then there is no need to do that.
To form from 6.8 SPC I cut them off to slightly more than the 1.250 case length using a cut-off wheel in a drill press and holding the case with a tap handle. There are as many ways of cutting them off as there are people shortening them. A CH-4D form/trim die would be a lot quicker and if I use .68 SPC brass again I will probably go that route.
Dies are CH-4D.
A quick trip through a sizer die with some Imperial Sizing Wax brings the case to shape.
Now a trip through an expander die so the trim pilot will enter the case without too much fuss. I suppose you could use the deprime/expander button but I prefer an M type die to expand in all my expanding operations. I have not used a decap pin mounted expander in decades.
Now trim them to the 'trim to' length, 1.250 inch.
Next you need to thin the necks. What I did was run them back through the sizer die (no expander button) to bring the OD to the proper dimensions, then inside neck ream with a Forster .328 actual diameter inside neck reamer. That leaves the neck wall the correct thickness so that when you expand the necks the walls will not be too thick to prevent chambering and proper bullet release.
Now another trip through the M die, prime, and load away.

Use standard rifle primers, large rifle if using Remington brass like I used, small rifle if using SSA brass or other brass using SR primers. I cannot imagine a situation where a magnum primer would be needed when using a rifle primer.