Hugh,
When the M16A2 was introduced, many of us felt it was not an improvement. The heavy match barrel made the rifle feel about the same weight loaded as the old M1 Garand. Additionally, it offered no real improvement in accuracy. I could argue that many shot worse, due to the additional weight. The need for a heavy barrel is non existent unless you are doing about 10 or so full auto mag dumps. The heavy barrel came to be when somebody, most likely the USMC, wanted to use a heavier grained bullet for further range and accuracy. Combat effectiveness was found to be reduced though. And now we have what we have in the M16A3, M16A4, and the M4 series. For most preppers I highly recommend a standard weight barrel, which most call a pencil weight. They are starting to make a comeback and for good reason. I went backwards also and my go-to AR is an old SP1 Colt collapsible. It works and weighs nothing. I got it cheap, as it has cosmetic blems on the receiver. Try a pencil weight; you can carry more ammo. – An old paratrooper