I had this happen years ago with Ammoman. I ordered M193 and he sent M855, which was actually more expensive than what I'd ordered. I called him up, mainly to see if he wanted it back and to ask another simple question, but before I could get past "You sent the wrong ammo", he blew a 20 amp fuse and called me every name but white. It was damn near comical listening to him. At one point I was tempted to call 911 and have them go observe him and make sure he wasn't having a heart attack or a stroke.
If your heart is set on XM193 I'd ask them to swap it out with them paying the shipping AND tossing in something to cover the headache. If you just wanted good ammo then ask for a partial refund. $200 should cover it.
If all else fails and you can't get satisfaction within a couple of weeks, reverse the charges and let him figure it out.