Monarch 45 ACP
I've shot steel case Monarch in a H&K USP Compact and a XD45 Compact without issue however I've seen some failures to feed Monarch and Tula steel in a few 1911s (Metro Arms, Rock Island, Kimber, Springfield GI) my old one included...
I've also hear Monarch steel shoots great in the M&P series and Glock pistols also...