As you might already know, dry firing certain rimfire arms can do serious damage to internal components such as the firing pin and the breech. Using “dummy rounds” or “snap caps” can help alleviate the risk of doing serious damage to your gun. However, finding a decent .22 LR snap cap is much easier on paper than it is in practice.
Here is the problem: unlike centerfire rounds that absorb the force of the firing pin through a thick polymer insert at the center of the case head, rimfire rounds crush a tiny and sometimes fragile molded or machined rim at the edge of the case head. This fragile head can be destroyed very quickly with even the most robust designs.
Unfortunately, these plastic Pachmayr .22 LR snap caps landed at the low end of this already-suffering bell curve of performance. Many of these rounds did not even survive the modest force of simply chambering the round in a bolt-action rifle. The steel extractor would simply shear off the tiny plastic rim, and it was over before it even started. I cannot imagine they would survive the violent force of a semi-auto action slamming shut on them.
Those that did survive the chambering and the wrath of the extractor were subsequently doomed at the first or second drop of the hammer, at which point the delicate plastic rim fractured and shed itself within the action. The core remnants proceeded to be pressed into the chamber throat and required a manual extraction via the cleaning rod.
In Pachmayr’s defense, I believe that we could just be asking way too much from this material, on a molecular level. However, these types of failures should have been readily apparent during prototyping and testing, and this product really should not have made it to the market without major changes.
While there are some more robust, aluminum .22 LR snap caps out there, polymers seem to make sense for this application. Aluminum will crush and permanently deform where polymer will flex and absorb. However, it must be the right kind of polymer, and the Pachmayr simply appears too brittle.