First off, don’t try this at home.
To test what happens when you fire a live round through a blank-firing adapter/attachment, in the above video Tim Harmsen with the Military Arms Channel sets up a throwback SP-1 type build with a period-correct $15 red BFA to see if the urban legends about it going kaboom are true.
For those lucky enough to never use a BFA, they are a common item in military service the world over for the past several generations, allowing a modicum of safety when using real firearms in exercises where you may want to fire at an opposing force during a war game. We say a modicum because they are generally just used to make gas-operated weapons cycle with reduced power blank rounds, not really stop a live round that was accidentally loaded, hence the subject of the test.
Of course, your mileage may vary and different countries have different types of BFAs, so you shouldn’t make it a point to find out which ones will stop a live round or not as that could be about as safe as vaping kerosene.
For a tour of some various BFAs, check out the below: