Re: AR Pistols
I see you've made your decision, but just in case someone else still wants to go that route...
I had a bushmaster carbon 15 pistol until this summer (sold it because it's simply not a practical firearm). Anyway, they used to have quick release removable muzzle devices. It was a collared device similar to what you find on an air compressor line for plugging in various different air tools. It was a pretty tight fit over the barrel, then three ball detents pushed into three recessed spots on the barrel when the collar was released. These QD devices were available without a muzzle device on them- allowing you to mount various different devices easily.
I believe the stopped building them as described above- not sure when, but they WERE built for MANY years with the above mentioned feature. Mine was reliable and fairly accurate (about 3" @100yds). But as others stated, it's really a novelty and its very limited as to practical use.