Quoted:
Why would someone want to mount a shotgun to the bottom of an AR? Why not just have a seperate AOW shotgun for breaching and a seperate AR? The concept is lost on me.
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You aren't the only one. Those that wanted and caused the KAC Masterkey came to the same decision and for the most part dropped the concept. They found it was not worth having such a heavy, overbalanced rifle, when it was only good for breaching doors. For the breacher, if that is all he did, I suppose it's okay, but it really made for a lousy rifle if he had to do anything more than that. I am guessing only a small few special purpose operators use it. As for civilians, the commercial version is not only really, really expensive, but requires an C3 tax stamp like any other machinegun, which can be problematic, and another $200 out of your pocket. It's only good if you have tons of money, toys, and want another toy to show off (unless your job requires it).