Okay, not trying to step on toes here OT but you are right and wrong at the same time. What you said about the firearm being able to put it back to semi operation in the field is correct. BUT you obviously haven't dealt with AR's or you would know putting a gas tube back in in the field is a bit more complicated than a simple field strip. It for damn sure aint something that "you could put back in or take out when you saw someone coming". Putting a plug back into a shotgun mag is quite a bit easier than the gas tube on an AR. Granted what mrbb was alluding to was sheer stupidity (I believe he said so himself) but he is in essence correct as far as the law goes. I personally can't see why anyone would want to do it myself other than just being a smartass as there is absolutely no advantage to a manually operated AR over anything.