I had an AC556 (actually I still have it, but I have a Form 4 in to the ATF to transfer it to the dealer to whom I sold it). It was my very first machine gun. Seemed like a great deal at the time, for all the reasons previously stated. Sure, it is a fun toy. Nevertheless, in the end, I sold it and bought an M16 (although selling the AC556 and buying the M16 happened in unrelated transactions, and not in that order ). Once I heard that Ruger was equivocating on servicing them I figured that was the last nail in the coffin.
If you can afford to buy something as utterly impractical as an AC556 you can probably also afford to spend a little less than twice as much and get an M16 lower receiver. You will be happy you did. There are simply so many more things you can do with an M16 -- so many high-quality uppers and accessories that are just made for it. Why get a conversion kit when you can just have a whole dedicated .22LR upper? Heck, there are even belt-fed uppers (the mythical Shrike, for instance -- I'm sure some day supply will catch up to demand). The ergonomics are great. And even though there is an element of absurdity when talking about the accuracy of a machine gun, you can still shoot it accurately in semi-auto.
You will just be much happier with an M16 in the end.
If you can afford to buy something as utterly impractical as an AC556 you can probably also afford to spend a little less than twice as much and get an M16 lower receiver. You will be happy you did. There are simply so many more things you can do with an M16 -- so many high-quality uppers and accessories that are just made for it. Why get a conversion kit when you can just have a whole dedicated .22LR upper? Heck, there are even belt-fed uppers (the mythical Shrike, for instance -- I'm sure some day supply will catch up to demand). The ergonomics are great. And even though there is an element of absurdity when talking about the accuracy of a machine gun, you can still shoot it accurately in semi-auto.
You will just be much happier with an M16 in the end.