Thanks Tracy

You mean they build up the gas pressure to that caused by live ammo, thus enabling the self-loading mechanism?

>That's a blank firing adapter. Blank ammunition will not normally cycle the actions of self loading firearms so a blank firing adapter that constricts the muzzle opening and builds up gas pressure to an operating level is installed.

...

>>Talking of which, what are those red things at the end of the barrel when on exercise? The British army use yellow ones. I presume they're to prevent the rifle from firing live ammo (but of course blanks can be fired) by some means, but I don't see how they work.