Buy a cheap packet of 7mm Sierra projectiles and assemble your fireforming ammo so it jams into the lands to keep that primer rearward as much as possible
Lightly lube the brass shoulder only with redding sizing wax to help fire form the shoulder should you chose a light powder charge
If you did not have excessive headspace then 15g of shotgun powder behind a one inch cleaning patch as a wad would have fireformed them.
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