I prefer Federal XM193 and a couple of days ago, just for kicks & giggles, to see if the M855 panic is crossing over, I did a Google search and was surprised to see it on sale (and in stock) in many places for about .40¢/rd. I was also surprised to see M855 on sale here and there, and still in stock.
The reason I prefer XM193 over M855/SS109 is because XM193 delivers more consistent terminal performance and it penetrates windshield glass better (ok, slightly better).
Regardless, I hope the OP got a good deal.