What was the round for the AR-15 orginally called and why was it changed?

Are you referring to the .224 (the actual calibre of the AR-15), but was changed to .223 because their was already a round of .224 that the army experimented with and rejected?  

nope

wasn't it a 222 at first, after it was scaled down from 7.62?

S.O.

your on the right track occifer but it wasnt scaled down from 7.62mm that was the round for the Ar-10

Damn i thought someone would be able to get it quicker than this this is after all a site dedicated to the AR-15

I meant it was the AR-10 in 7.62 at first, but the rifle was redesigned and scaled down around the 222.

S.O.

ok but what was the full stamp on the round 222 is right but there is some more

That, I dont remember.

S.O.

yes

this one might stump you. what was it called after the crtridge was lengthed to get the desired velocity?

7.62
Magazine capacity?

It was originally referred to as .222 Special, which was the version produced for Gene Stoner from the specs for the last version of Aberdeen Proving Ground's SCHV experimental ammo. Since there was already .222 Rem, and there were plans for .222 Rem Mag (intended to be a civilian version of the SCHV) they later changed the name to .223 Rem before commercial and military sales of the AR15 began. BTW, the .223 was not a scaled down or necked down anything - it was based on the .222 Rem, but with increased case capacity and a heavier and specifically different projectile. It very nearly never saw the light of day thanks to one Dr. Fred Carten and his championing of the 7.62x51 as the only battle cartridge needed, despite the fact that the SCHV was intended by its original designers as a replacement for .30 carbine and all subguns, not as a main battle rifle cartridge.

.222 Rem Mag quickly became obsolete when the military adopted .223, and is no longer available.

and interestingly the .223 is actually.224

did u guys know that the viet cong coud use m16 rounds in their rifless?

They "could" if they only wanted to fire 1 shot.  This was discussed and tried not to long ago.  It woirked in firing the cartridge, but it didnt cycle the operating system.