What is this stuff?  I bought a box at a gun show today.  Is it AP?  Any idea of what it'll go through????

It's M855.  It has a steel penetrator, but it's not really classified AP.  It won't really go thru much more than standard M193.

Green tip is not officially AP. If it was, we (US forces) could not use it for anti-personnel purposes as per the Geneva Convention... However, it will penetrate steel(I've seen it blow through 1/4" steel). It weighs 62 grains and was originally designed for use in the M-16
A2. It is called M-855 by the US military and is known elswhere as SS-109. Good ammo, but don't expect much in the way of accuracy through a 1/12 barrel. Through 1/7" and 1/9" it is quite accurate.

& it's 5.56mm, not .223 cal.

Quoted: Green tip is not officially AP. If it was, we (US forces) could not use it for anti-personnel purposes as per the Geneva Convention... However, it will penetrate steel(I've seen it blow through 1/4" steel). It weighs 62 grains and was originally designed for use in the M-16 A2. It is called M-855 by the US military and is known elswhere as SS-109. Good ammo, but don't expect much in the way of accuracy through a 1/12 barrel. Through 1/7" and 1/9" it is quite accurate.

The Geneva Convention is a common misunderstanding, the Hague convention in 1899 declared so called "dum dum"(a METAL jacketed projectile with the lead core exposed on it's POINT, or the jacket weakened with slashes/incisions) projectiles forbidden, the use of AP ammunition against living force isn´t forbidden anywhere i believe.

The most commonly issued rifle ammunition during the second half of WW2 was M2 AP.  There are no treaty prohibitations against it againt personnel.

Regardless, M855 Ball isn't AP anyway.  

-- Chuck