The biggest problem is the muzzle brake, if you plan on shooting them you need to remove it or risk damaging it. Plus if it opens inside the brake and it sends pieces flying, you could be sued by other shooters that get hit by the pieces and injured. There's alot of forces at play with the .50 and getting hit by shrapnel is gonna leave a mark. If you've ever been sitting next to someone shooting a .50 and get hit by a piece of unburnt powder you know what I mean.

Another issue is getting them to chamber, most .50's can't chamber them due to the design. Now think about what's going to happen to that plastic sabot if you force it into the chamber to try to shoot it.

Lastly is the price, most sell for about $20 or so EACH, most people just want one for the collection and that's about it.

Are they available now, without being stolen?  

Yes, you can get them.

I doubt any of it's stolen, I think that most of it gets to the market from companies that get it from the government for testing. They use X amount for whatever tests they do on armor or... then end up with some left over. Most will just keep it and use it if they feel the need but you have some that will just throw it up on the auction boards.

So technically it's not stolen, they just never returned the un-used ammo and saw a way to make a profit off the government. [>:/]

So, I was looking for something totally different and I found this thread about SLAP ammo from Gale McMillan.

http://yarchive.net/gun/rifle/50bmg_sabot.html

Ah, thanks!