Re: AR 15 barrel length question?
if 4" is plenty good at 100, you could easily use a 6" barrel! my 10.5 shorty did some good work out to 400+ meters with no problem with accuracy or velocity. sniper gun? nope. but it will print an easy 1.5 MOA with military green tip, probably less if human error was removed.
16" is plenty of length to achieve 1 MOA IMO, good velocity also.
"Loud noises don't end gunfights.... well placed shots do."