Need advise from gurus who perfected the art of fireforming.
I've successfully resized 7.62x39 brass & fireformed to 6.5Grendel wihtout seating all the way to the rifling since it still headspaces partially on shoulder.
On the 9x39 however, the tapered wall of the 7.62 puts the shoulder just a tad wider than the neck of the 9x39 chamber that loading it on an AR pushes the round forward that the extractor doesn't engaged the case head & jams. Manually engaging the round to the extractor prior to chambering forces the round to headspace from the casehead & will work but it'll be tedious even on a sidecharging upper..
Any insight is appreciated.