tracker and Tom,
I just recently got a Bushmaster AR-15, so my knowledge is fairly light.
Most of the AR-15 rifles seem to be rated for 5.56mm, which M193 is. You can shoot .223 in that rifle, if it is rated for 5.56, but the reverse is not true.
M193 is a NATO round which packs more of a wallop for military use, as compared to the .223. It should make more noise, flash, and recoil.
I think if all the experts got together, and had to recommend something to buy, they would recommend the XM193 as an excellent choice for someone who needs guidance.
Here is an outstanding reference:
http://www.ammo-oracle.com/body.htmThe prefix X is attached when the ammo is sold to civilians.
Many, perhaps most, people prefer to buy the Federal ammo from Lake City.
I intend to have 1000-2000 of XM193 on hand in case of civil disorder, bad people, and other requirements.
I'm finding that more and more advisors are recommending the AR-15 for home defense.
If friend and foe are near each other, the AR-15 would be more accurate than a shotgun. Also, you might have to step outside during a violent encounter. XM193 should be more than adequate.
In addition, we frequently read that the AR-15 may do less dangerous penetration through walls than a pistol.
Do not buy XM193PD. It is generally to be avoided, according to my readings.
Bill