Sorry - didn't want to sound negative, but sometimes reality hurts. Ball and AP projectiles have not been manufactured for a long time and with the up-surge of 50BMG shooters like us, they are near impossible to find at reasonable prices. In years past I bought 3000 AP's but sold about 2500 of them at a ridiculous low price to fellow FCSA shooters.
I bought a 50cal can full of API for $100, never counted them but think I got a good deal. As a responsible shooter, I am very careful on where I shoot them. Must be after a rain or with a very good backstop which will not have any burnable massterials in its construction.
A few years ago, South African ball which weighed 695 grains were available. I have a few left.
US Ball, SA Ball, AP, API, APIT, and other 50Cal projectiles almost always have a steel core of some type under the copper shell. Some ranges will not allow steel core projectiles as their way of restricting 50BMG on their ranges.
Brass ball projectiles are available from Lehigh Products. P/N: 510-120 which weigh 650 grains. I use them with 245 grains of H50BMG powder. A near max loading = be careful and work it up in your firearm.
Mostly for Match loadings I use the 510-170's which weigh 808 grains - they will not fit a magazine as length is in excess of 6".