Originally Posted by DJ's left nut
Well hell - if it's a 16 inch barrel, you essentially have an AR. The true distinction between an AR and an M4 is that the M4 is select-fire and has a 14.5 inch barrel.
Otherwise, if its a civilian rifle built on an M-16 platform, it's an AR. If you slap a 20 inch barrel on it, I'd simply call it a 'target' AR. The 20 inch barrels are more of an exception rather than the rule, in my experience.
What you've got there is an AR-15.
I had a small discussion with my customer on that point. This rifle basically has an M4 upper, which he said was built to handle full auto fire reliably.