Binko,
If you mean you will make them from a grade 8 bolt, that should work o.k.. But, there are better choices if you have the ability to heat treat and/or have access to other materials. Grade 8 refers only to the tensile strength (150,000 psi in this case, equating to about 40 RC hardness) and the alloy remains somewhat optional to the manufacturer. Cheap grade 8 bolts will be made from low alloy steel with moderate carbon content to get it to harden during heat treat. Fracture and fatigue characteristics of a hardwarestore grade 8 won't likely come close to an aircraft quality grade 8 bolt. There are other specs to control aircraft bolts that specify these other characteristics.
Nevertheless, a common grade 8 bolt is better than a piece of mild steel for what you're doing. The 40 RC hardness is about as soft as you may be able to get away with. On a low usage gun, it should be fine. On a Perazzi target gun that will see tens of thousands of rounds, it'd be a temporary fix for the firing pins.
