Has anyone had a pre-64 model 70 misfire intermittently with all different types of ammo? almost like the firing pin is broke, But the bolt was totally gone over by Hart rifles, so i doubt its the bolt.
I suggest you remove the firing pin and spring assembly from the bolt (safety in center position) and clean it thoroughly. Spray some degreaser down the inside of the bolt and make sure no old grease is present. Then wipe the bolt and firing pin spring with an oily cloth or patch - don't add any "liquid" or grease lubricant - and reassemble. This has cured more Winchester, Remington and Mauser-style bolts than I can count. -Ed
As said above pull the bolt apart and inspect. The possibilities are gunk, a broken spring or a bent/broken pin. The problem should be obvious once you get the bolt disassembled and once resolved, the rifle can be expected to fire all ammo/primer brands in all conditions.