The Vietnam War-era M16A1 rifle weighed in at around 6.5 pounds, a little over 7.5 loaded, depending on accessories carried [sling, cleaning kit in butt, etc] The original milled-receiver AK-47 weighed 4.3 kg [9.5 lb] with an empty magazine in place, the later AKM stamped-receiver version introduced around 1960 3.14 kg empty, about 7 pounds even. Weight of the loaded 30-round magazine is .6 kg, about a pound and a half.
The AK47 and AKM however, have 16-inch barrels, making them really more an equivalent of the Vietnam War period XM177 *Car15* or the current M4 carbine [weight, 2.52 kg/ 5.56 pounds empty, 3.0 kg/ 6.6 lb with loaded 30 round magazine] The M16A1 had a 20-inch barrel [and better sights] part of the reason for its better accuracy and longer range. Those desiring accuracy from the Kalishnikov platform use the RPK version with its 24-inch long barrel and bipod, accurate on human targets well beyond 500 meters if things aren't too windy...under which condition the 55-grain M193 ammunition of the M16A1 is no great performer either.
The current M16A2 also has a 20-inch long barrel, but of heavier thickness, increasing its weight to about 9 pounds/ 4kg. Accordingly, the now-heavier M16A2 rifle and the now lighter former Soviet AKM weigh about the same, though variations in magazine capacity, accessories, magazine construction [aluminum, steel and plastic magazines are around for both weapons] can tip the scales half a pound or so either way for either rifle.
Online AK captured enemy equipment manual *here*
Interesting Vietnam-era M16 *comic book manual* *here*
