Are there details or backstory on this ammo?

Hornady frontier. But for fitty cals.

We had 4 or 5000 rds at Barrett long ago. Some summer help was brought in just to pull it down. Destroyed the shoulder of the brass with a hammer, oiled the powder and tossed the projectiles.

That's some ugly ammo!

I asked for and was given one round by a friend.  Just to keep as a sample.  The yellow paint is half scratched off, the brass itself looks weird...  

I don’t even know if the components themselves are truly usable.

Brass: Known to split easily.  Weird “flow” to the brass.  Odd lengths and primer pockets.  Sometimes you’ll line up a bunch and the shoulders are notably different.  Case necks might not be straight.

Powder:  Irredeemable.

Primers:  May be in a bad primer pocket.  Some don’t fire and others fire as of BMG “magnum” primers are a thing.

Projectile:  Multiple different grain weights.  AP, so may be an issue shooting at some ranges.

Some of the projectiles we pulled had loose cores inside the jackets. You could shake the bullet and feel the core moving around inside the jacket.
Some projectiles had the lead seal at the base , a lot didn't.

Supposedly it was stored in a location where it became damp, then tarnished, and was tumbled long enough to not only clean it up nice and pretty, but also break the powder down into smaller kernels, thus changing the burn rate. The tips were repainted, and it was shipped to the US where it proceeded to blow up a few guns.

Lucky me, I just got 20 or 30 rounds of it in a large lot of ammo.