Bought first AR-15(colt 6920) from a friend. New to the world of 223/5.56. Searched the resource links re ammo rating, etc. Lots of discussion about 3131 vs.3131A, Federal 193(with all the letters before and after#193),etc.,but I cannot find a single posting that explains the actual differences other than where ammo is manufactured––Isreal, Lake City––who manufactures it––Federal, Winchester, PVC, etc.
The ratings and review posting gives one a sense of reliability but is there any one location that explains differences in some detail vs. having to search each ammo type individually to educate oneself?

Try This:  Frequently Asked Questions

and Specifically:  Ammo Oracle

Or the Downloadable version:
Ammo Oracle PDF


ETA: I can't believe I beat Zhukov... He must be celebrating the HOLIDAYS

As recommended, definitely give the Ammo Oracle pages a read, fantastic info about .223 and 5.56.  

Thanks.  Must have skipped over the Ammo Oracle posting––although the FAQs certainly told me where to start!  Now I know just enough to keep up with the conversation at the range, but I still have much to absorb.

Yes young Padawan... there is much to learn.

Absorb it you must

Padawan in 5.56 but next level up in .45, 9mm, 220 swift(for those old enough to remember) and the ancient .22lr––especially with a Winchester M52.