I've become obsessed with AR-47s in the last few years because look at this thing. Apparently 7.62x39 is the far better caliber for pistol builds: because it's energy comes from that fat cartridge, it doesn't depend on barrel length to get up to speed the way 5.56 does, so it loses very little out of a shorter barrel. All the spare powder makes a big sweet fireball too.

Obviously the challenges of rechambering the AR15 upper are all related to the size of the new cartridge and the stresses it puts on the finer parts. AR-47 bolt carriers are typically made from tougher materials to compensate for the higher pressures, as are the firing pin and extractor.

According to a bunch of gun review sites, a well-built and tuned one of these feels like the best of both worlds: the ergonomics, accuracy and reliability of a modern AR-15 combined with the 123-grain smashing power of an AK-47