I just noticed these new snap caps for the first time. They are called striker-caps, and are designed for striker-fired pistols which call for having the slide pulled back before the trigger will function on the firing pin. I didn’t know this was much of a concern, but apparently there is a market for these rimless things. As to how one removes them when done, they don’t say, but people are presuming a push-rod from the muzzle end? They have multiple calibers.