Even if you are someone that get’s very accurate results from your M4 or 14.7 inch barrel AR15.   You may be getting hits, but that caliber can become very weak once you get several hundred yards out.   When I picked up a chronograph I was blown away by how much velocity I actually got out of short barrel handguns and my M4 rifles because it did not match up with what I previously read about on the internet.   I saw 75gr HPBT clock at 2900fps out of my guns when I thought they would have been close to 2750.   I know you can push the limits with hand loaded ammunition, but you do have to be careful about excessive wear and tear.

I have been recently thinking about picking up an LWRCI Repr because I have been a big fan of battle rifles and even the military has brought back the 7.62 DMR rifle in various configurations.  I have even seen a few British troops show up with FAL rifles with scopes on them.   There is also a difference between what you can get out of a 55gr hpbt and a 75gr hpbt out of a 5.56 gun.  Sometimes an 18-20 inch AR15 upper receivers will get you far more range and punch than M193 ball ammo.  What you can do at 400-800yds with those guns compared to a 55gr bullet is considerable especially with wind drift ect.   Of course much of this is up to the skill level of the shooter.