Best AR-15 fixed magazine for easy removal?
What's the most easily detached fixed magazine that isn't, erm, a detachable magazine? I'm looking for something that can easily be removed and added back in when I go between DC and VA. Apparently, a Maglatch FNGR fixed magazine can be removed in seconds after the upper is separated from the lower. That would be ideal, but without further guidance on what it means for a rifle to have "the capacity to accept a detachable magazine," I have to wonder if the MPD might say that's too detachable.
I guess this is more of a philosophical question than a request for product recommendations. If a detachable magazine is locked into a receiver in such a way that it can't be removed without separating the upper and lower, is the rifle capable of accepting a detachable magazine? What's a reasonable dividing line? What would the average MPD officer think?
For context: I already have a few stripped lowers that are registered with MPD, so this is less about what MPD might approve at registration and more about what they might object to after the fact.