Most of the time it's not the shells it a the firing pin, is dirty a good cleaning and it works good. It is always good to cleaning the firing pin. Was it a little dimple on the primer. If so I think I the firing pin and spring is dirty a good cleaning would work wonder ful. That happens a year a go to my dad and his 35 Whalen. Firing pin and spring where so junked up they were real sluggish a good cleaning and no problems.