Well, even with a firing pin stop in place the pin it is still "stopping" on that stop, not on the snap cap. A rimfire snap cap will be beat to death shortly if the pin is hitting it every time. In my experience the only snap cap to use on a rimfire is an empty case turned so that it will be struck on a virgin part of the rim. After 2 or 3 hits it's trashed and isn't really helping.