Snap caps are awesome for weeding out bad mags as well, but you need at least 3-4, as it's the last 2-3 rounds that seem to cause problems.
Generally 22LR rimfire is bad to dryfire, but alot of centerfire rifles can take it. There are always exceptions to this, but 22LR is almost always a bad idea to dryfire.
HMC- Snapcaps are plastic bullets, with a spring and metal button where the primer is, so the firing pin impacts the button and has a gentler impact as the spring simulates the give of a primer being hit. They are pricy, around $8-$11 for two .223