I've been shooting for 45 years. Never owned a snap cap until this year, because of Kel Tec. I've always used spent shells. Never had a problem with firing pins etc. I bought 9mm snap caps for the Kel Tec and it hit the plunger so hard it drove it in so deep it would not reset. What's the concensus on using spent shells? I use them until they look bad then swith to another. I don't dry fire without something in the chamber. Either a spent shell or snap cap. I know there are exceptions, but exceptions confuse me and I stick to one rule.