Is it potato or potatoe?
I don't think there is any need to get wrapped around the axle with semantics. I too initially thought the thread was about a battle drill type reaction to a threat. However, the Army still teaches new soldiers to perform immediate action when their weapon malfunctions. Now that we've determined we're talking about immediate action to clear a malfunction. lets get back to that subject.
Everyone who employs a semi-automatic weapon for defensive use needs to know the drills to clear it, should it malfunction. I've found the simplest method is to transition to the BUG, stay in the fight and worry about clearing it later. This might not be the best option if you're in a fight at any distance and your long gun goes down though. You may be out of effective range of your BUG.
I think that the best method is always to train as you intend to fight. Like strambo, at arms distance I'm transitioning to a hard hand combative (center punching the assailant with the handgun, muzzle strike or buttstroke with a long gun), just out of arms reach to 25 yards, I'm moving and transitioning to the BUG, 26 yards and farther I'm clearing my primary weapon and getting it back into the fight.
A safety note: When you are practicing malfunction drills, remember to listen for any difference in the sound of your weapon and feel any change in recoil. Pop, tap-rack-bang can equal KABOOM if the squibb load lodges the bullet far enough down the barrel to allow you to chamber the next round. I very nearly blew my Colt R6920 up like that at Pat Rogers' carbine course last summer. I was concentrating on the problem (a box drill at 26 yards IIRC) when I had the squibb load. Didn't notice any difference in the sound, and the load was enough to cycle the bolt. I dropped the magazine, racked the bolt three times (since the bolt cycled, I figured the case tore or the extractor pulled off the rim) put in a fresh mag and attempted to chamber a round and get back in the fight. The round wouldn't chamber. I was so intent on finishing the drill, I hit the forward assist when the new round wouldn't chamber. Needless to say, if I had been able to chamber the next round, I would have blown my carbine up, possibly injuring myself and other shooters on the line.
Jeff