That’s not really what BFAs do, at least not the models I’ve used. You seem to imply that weapons with BFAs fitted are still firing real rounds, which are rendered safe by hitting the adapter. That’s not true. They are firing blanks, which are cartridges with the bullet and some of the powder removed. Pull the trigger, you get a pop, a flash, and some smoke. Yay!
Pull the trigger again though, and you’re very likely to have a misfire because the next round failed to feed from the magazine to the chamber. This is because most semi or fully automatic weapons use some of the energy of a fired round to cycle the action which expels the spent cartridge and feeds a fresh round into the firing chamber. When you fire a real bullet, it actually acts as something of a plug in the barrel for the very brief period of time it travels through it. This allows the pressure to overcome the resistance of the weapon’s action, and thus operate.
When you fire a blank, there’s no bullet. No bullet means no plug, which means that all of the gas from the explosion just rushes right out the end of the barrel and is not enough to cycle the gun. This, you have to manually run the action, turning your scary big black assault rifle into a quaint bolt action rifle.
So, how do you solve this problem? You make your own plug and stick it on the end of the barrel to redirect all of the energy through the weapon system rather than expelling it. That’s a all a BFA is, a metal post matched to the diameter of the barrel that screws into place to plug it. This has the additional positive of preventing anything from exiting the barrel accidentally while firing blanks, which is useful in the training contexts that you often see these devices, because you’re often “firing” on other people.
If you were to use a BFA in the manner you describe, i.e. with a real bullet, you’re certainly going to damage the shit out of your weapon, and possibly wind up in the Emergency Room because you caught some metal splinters in the face when the end of your weapon exploded.