There is an A&D AM180 Drum adapters for the AR15/M16 are available. There will be other adapters comming for other rifles.
They have one hundred units available.The price for one to five units is $284 including shipping.
They are offering quantity discounts for purchases of more than five units.
Here is a video of it in action: Bazooka Brothers Mfg.
Bazooka Brothers Mfg.
Specializing in Pistol Cal. Conversions
And here is where you can get the drums the cheapest that I know of.
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