50 cal ammo is going to start getting really hard to find soon, even the slugs to reload your old brass will become non existant. Keep your brass and see if you can form a ceramic mold to make your own slugs, but some of the AP rounds would be really hard to make, may have to electro plate the slug to get an even coating so the bullet flys right. Also most AP rounds have a tungsten core which would have to be machined perfectly otherwise your round would tumble.
I may start hoarding 50 cal brass in case I some day get a barrett M82. May be able to build a laser to machine the hardened metal parts of the AP core since the temps required to cast tungsten is quite high, you can buy ovens that get up to like 4-5k F that are used to fabricate micro electronics but they are like 5 grand but they are not very big.