what size caliber bullet goes into the .223? is it a 22cal? with 50-75 grain?

Like everyone has said .224 caliber bullet. If you are reloading, the heavier bullets are longer. They may not fit in an AR.

A .223 fires a .224 diameter caliber jacketed bullet. Typical grain weights are: 40, 45, 50, 52, 55, 62, & 70.

0.224 - same diameter of bullet used for:

.22 rimfire (S, L, LR, EL)

.22 WMR

.223 Remington

5.56 nato (this is really just a 223 at a higher pressure)

22-250

.222 Remington

for .223 Remington typically a 55 or 62 gram FMJ bullet, or 62 grain JSP, 55 grain JHP.

for 5.56 NATO you'll see either the 62 grain XM193 or 62 grain XM855. the military has opted for the 62 grain weight for better terminal ballistics.

224

No, the velocity of a .50 BMG cartridge is not even a significant percentage of escape velocity. Doc Hudson

Yes It's a .224 dia. bullet, and weights are offered ranging from 45 to 75. gr.s.

The 'twist' of the particular rifle that uses it will determine how heavy a bullet

may be used and still be stabilized.

Don't load more than 55 Gr. bullets for a 9" twist rifle..

And --- Be sure to look over this .223 cartridge guide......

http://www.6mmbr.com/223Rem.html

Ditto exactly what is said above. .224.