“The 5.56 uses a slow rate of rifling to keep the bullet barely stable during flight. The slow rotation allows the bullet to tumble when it strikes soft tissue and cause more damage. The slow rotation and ultra velocity combine to cause the bullets to fragment or tumble if they hit anything during travel.”
Current standards are 1x9 for the A2 and 1x7 for the M4. The slow twist/light bullet/tumble thing dates back to the early models. 77 grain Mk262 ammunition is supposed to be available for longer ranges.
As for the comment that our rifles should have been cleaned - we didn't have the chance. Our weapons weren't issued to us until the last minute and we weren't given the opportunity to fire it until we were attacked. Having a light coating of oil doesn't mean the weapon is dirty. That's the way they were kept to prevent rust.
When I entered the military in '74 most of the older guys were badmouthing the M-16. I had several negative experiences with them that have undoubtedly tainted my opinion.
On the other hand, there have been numerous test and evaluations and enough anecdotal accounts to come to a reliable decision that the M-16 is not the best weapon for the money. Units that are allowed to select their own weapons, like special operations, almost always select a more reliable weapon. Many of them pulled M-14s out of storage and used them and some are using HKs.