Are AP rounds legal in Kalifornia?  Are they legal to buy new?  Is this just the bullet, or the whole cartridge?  Are they legal in .50 BMG as well?  

Details please...

Thanks

.50 BMG AP is legal because there are no pistols chambered for it. If there were it would be banned the next day. All the fun stuff like API, APIT and the like are banned.

Most of the ranges don't allow steel core (ball .50 BMG has a steel core also) ammo to be fired due to the high fire risk. That and the fact that it really beats the shit out of their targets.

i thought all true ap ammo is banned in cali.

IIRC only pistol caliber AP is not legal to possess.   Refer to Ca. penal code sections:

12320. Any person, firm, or corporation who, within this state knowingly possesses any handgun ammunition designed primarily to penetrate metal or armor is guilty of a public offense and upon conviction thereof shall be punished by imprisonment in the state prison or in the county jail for a term not to exceed one year, or by a fine not to exceed five thousand dollars ($5,000), or by both such fine and imprisonment.

12323. As used in this chapter, the following definitions shall apply:
(a) "Handgun ammunition" means ammunition principally for use in pistols, revolvers, and other firearms capable of being concealed upon the person, as defined in subdivision (a) of Section 12001, notwithstanding that the ammunition may also be used in some rifles.
(b) "Handgun ammunition designed primarily to penetrate metal or armor" means any ammunition, except a shotgun shell or ammunition primarily designed for use in rifles, that is designed primarily to penetrate a body vest or body shield, and has either of the following characteristics:
(1) Has projectile or projectile core constructed entirely, excluding the presence of traces of other substances, from one or a combination of tungsten alloys, steel, iron, brass, beryllium copper, or depleted uranium, or any equivalent material of similar density or hardness.
(2) Is primarily manufactured or designed, by virtue of its shape, cross-sectional density, or any coating applied thereto, including, but not limited to, ammunition commonly known as "KTW ammunition," to breach or penetrate a body vest or body shield when fired from a pistol, revolver, or other firearm capable of being concealed upon the person.

Quoted: i thought all true ap ammo is banned in cali.

Nope, not at all. It's TRACER ammo that's completely banned here.

Quoted: Nope, not at all. It's TRACER ammo that's completely banned here.

Not all tracer ammo.

It's shotgun tracer ammo that is ok, right?

Quoted: It's shotgun tracer ammo that is ok, right?

Yupp