Among Afghans, AK-47s are so ubiquitous that we referred to them as Male Jewelry. Adult males in the tribal areas wouldn't leave home without them. And no, we didn't confiscate them...which would have been a silly waste of time and a good way to alienate the very folks we were allied with.
Crew served, ground-to-air threats, caches...yeah, we'd grab all that and dispose of it.
Large weapon caches saw us recovering everything from Milan wire-guided anti-tank missiles to black powder Jezzails. I'm talking average hauls of 10-15 semi-tractor trailer loads of armaments typically pulled out of single holes in the ground, "basements", or caves.
One of our guys re-conditioned a water-cooled 1906 Maxim and integrated it into our firebase defense. He used parts from 4 guns, had the locals go find some cloth belts of German WWI ammo (paid a bounty), and the gun was good to go.
An OGA friend (former SF guy) carried a very nice Thompson 1928A1 for his entire tour.
Several of us carried Makarovs as BUGs.
The only "modern" scavenged weapons adopted in quantity by members of my unit were PKM machine guns. Great weapons and a handy way to plus-up small unit fire-power.
The reason for the eclectic weaponry present in Afghanistan is that every international arms dealer in the world divested themselves of stockpiled ancient weaponry during the era of the Soviet invasion. The US, Pakistan, and certain Arab states underwrote arming the Mujaheddin. In response, shiploads of otherwise unsalable and obsolescent arms were moved to the region with a will. In most cases, exactly what was being delivered was not carefully scrutinized. Many millions of dollars were involved, and certain customers got taken to the cleaners by unscrupulous holders of end-user certificates.
Remember the scene in
Uncommon Valor, where the US mercenaries lose their high speed gear in Thailand, confiscated by the authorities? They resort to re-equipping from a local small arms black market. Having limited funds, they are taken to dusty crates of bargain basement WWII small arms.
All the ones Gene Hackman and his movie buddies didn't buy? Shipped to Afghanistan...from everywhere in the world. Seriously.