Interesting. The double feed drill I learned involves locking the bolt to the rear, dropping the magazine, fingering out the stuck rounds, racking the weapon 3 times, then inserting a fresh magazine. Especially now that we use the ACOG optical system on our rifles, I'm not too keen on the idea of beating that thing against the ground. Maybe with an M14 or something similar, but I've never run into a jam on the A4 that I couldn't clear this way.
I will say that the two weapons I've handled that had collapsible stocks (the M4 and the M1014) both would have held up to having the stock slammed into the ground.