One should fire form the brass to the gun it will eventually shoot. Otherwise, one may end up with brass that won't chamber in the intended gun. I did a lot of fire forming 5.56 brass to shoot 7 mm rounds out of a Thompson Contender in IHMSA competition. I'd be surprised if chamber pressures were higher fire forming than when pushing a 7 mm 162 gr boattailed Sierra downrange. Stan, you are welcome to use my Baikal single shot if you want to go that route. Gil