LOL! That is hilarious. Biden as usual with absolutely no idea. The AR-15 is a 'civilian' derivative of the military M-16. The M-16 was developed during the Vietnam War for the US military - as a competent weapon at normal combat ranges - 100 to 200 metres. It was also very good in close, light-weight, quick to raise - and sight (if sighting is needed) - M-16 is pretty good. Compared to a shotgun (I am assuming 12 gauge) - which is slower to raise, the shotgun makes a bigger hole. But, you have to hit the target. AR-15 standard mag is 20 rounds. The bullets come out as fast as you squeeze the trigger. With the selectable fully auto M-16 - they come out much faster. The 12-gauge is best for requesting entry into premises. The AR-15 is more useful inside for taking out the trash. Personally, for American rifles, I find the M-14 does the trick. Nice size 7.62's, it feels like a rifle, it works like a rifle, but it is for someone tall like me - the right size to bring up and get to work. At a distance I also shoot much better with it. Less wind and natural drop/distance issues.
