A gun? I'd be more accurate with a ruler!

The only difference is 0.003" (that's 3 thousandths of an inch) in the diameter of the projectile, and the amount of powder behind it.

A few questions - What is the difference in barrel length? What is the difference in weight? What is the difference in kickback/recoil? This is what I learned - "The AR-15 series is designed to absorb the recoil by the large recoil spring in the stock. Therefore giving the AR-15 series more accuracy and more control by just about anyone who fires it." My thoughts are this is what makes it the choice for these events. My issue is that The AR-15 is too good, too perfect for these situations.

Barrel length is variable depending on which model you get. This one appears to be about 18", but regulations limit how short a barrel can be to 16". Weight on this one would probably be comparable to an AR due to the wooden stock am heavy barrel, but a synthetic stock with a sporter profile barrel would be lighter. The recoil would be close to comparable with the AR on the lighter (synthetic) version and probably less on the one shown.
All semi-automatic rifles and shotguns have springs that are comparable to the recoil of the weapon. This is a mandatory item to make it operate (self loading). An extra benefit of it is the lessening of the felt recoil. I am sure the lessening of the felt recoil assisted my fellow Texan in thwarting the plans of the church shooter and ending his life, pictured in my other comment.

Thanks again for the good info. I was watching a video but the comparisons were not equal. It was shotguns vrs ARs. There was no comparison.

There is a much bigger difference between shotguns and AR's, but there are semi automatic shotguns as well. I have shotguns for bird hunting (dove & quail) and a shorter one for home defense. The shotgun makes a very distinct sound that everyone knows and could be heard when loading through our entire house. So if you load that weapon and then proceed through the house, no one in there right mind will remain in the house having heard that, which means if they are still there, they are there for bad intentions and should be shot. That is my perspective on home defense. In short, "the lock on the door you just kicked in, is there to protect you, not me".

YUP!