There is a reason that there are 12 in the pack - Traditions Rifle Snap Caps, .22-.17 HMR

5 of these are in my case with my .17 HMR and one in the chamber. 5 more are in the case with my .22 LR and one is in the chamber. Being made of plastic and so small, they do the job, but you will quickly use up one and need to use another due to dents in the plastic. This is fine for guns that are easy extracting cartridges. They do what they are intended to do while being inexpensive. For auti handguns, I have gone back to using spent .22 cases. I am not sure that there could be any better design for these, so I will keep buying them as the older ones wear out.