Although the Russian Kalashnikov assault rifle is the one that is most famous, it is arguably the Chinese Type 56 AK that made the bigger impression on the world in the 1960s and 70s. This rifle was initially developed with Russian technical assistance just before the Sino-Soviet split beginning in 1956, but subsequent development took place without Russian input, leading to an entire family of unique AK variants. The name “Type 56” actually refers to this entire family of Chinese AKs, which includes milled receiver variants derived from the Russian Type 2 AK, as well as stamped versions similar to (but distinct from) the AKM. These guns showed up all over the world, and for many they are THE iconic “AK-47”. They were the primary weapon of the North Vietnamese Army in the latter half of the Vietnam War, were exported by the Chinese to Africa, Asia , and South America. It was the most used AK variant by the mujahideen during the Soviet-Afghan War, up against Russian AK-74 rifles. Too this day remains one of the most common if not the most common AK variant, and it’s the Chinese Type 56 with its distinctive integral spike bayonet that is famously depicted as a symbol of liberation on the Flag of Mozambique.
So, they had a pencil barrel AKM versus a heavier barrel AR. Even if the out-side diameter of the barrels were the same, the AR barrel was still thicker because the .223 caliber is smaller than the .310 caliber of the AK. So, a heavy barrel will always outlast a thinner barrel. Also, the AR had a open, free-float hand-guard that allowed more air to reach the barrel. The AKM uses thick wood hand guards that insulate the barrel and hold the heat in. Seems like it wasn’t an even playing field to start with. Try a pencil AR barrel and put a open tube hand guard on the AKM and try it again. My guess is, with conditions closer together, the difference would be much closer. In either event, neither gun was designed as a machine gun. Real machine guns have heavy barrels that can be switched out easier. AND was he able to get the AR back in service by banging in on a tree like he did the AKM? NOPE.