Saw this on the outdoor channel. Thought they were cool. Not sure how easy the ammo is to come by.
Shit forgot to post the link lmao. http://www.impactguns.com/store/AR-57URSBR.html
The 5.7 is an expensive caliber to shoot. At least on my budget. http://www.ammoengine.com/find/ammo/5.7x28mm
Prices start around 40 cents per round, will be lower if you reload. The Ar57 Upper or a PS90 are great guns. I have worked with a AR57 upper, loved the fact that you can modify a standard 30 or 40 round M4 mag in the normal AR-15 mag well to catch all the brass. Great for when you want to reload don't have to worry about picking up the brass.
its not cheap and all the good AP ammo is "restricted". You can still find vendors selling it every once in a while, but it will cost you your first born
Yes it is difficult for find AP ammo in 5.7 by 28. AP ammo can be made by reloading the ammo. Using the same AP bullets as you would for 5.56 or .223