"Has a 22 made a combat insertion, extraction, or medavac to/from a hasty LZ under fire?"
We did qualification on M4 rifles from our aircraft a while back. We hit more targets than several other units which had mounted machine guns. We also did dozens and dozens of hot zone medevacs and had 1 round hit an aircraft, with no injuries. Tactics are the key here. Aside from that, those who do the medevac stuff agree that every extra knot you can get when en route to or from the injured guy counts more than anything else.
Many of our sister units did hot inserts and extractions for the infantry guys, and none of them fired a single covering fire round. War has changed, and while vietnam meant huge amounts of covering fire, the current war means speed and agility getting the guys on the ground, more than having a blast of machine gun when you're rolling in. If you need the heavy cover, mount up the miniguns and bring some guns with you, but if it's the typical assault they're doing these days, the ability to jump 60 miles in 20 minutes instead of 30 is way more influential than a few rounds leaping from the heli on the way in.
-Mike