Most AR500 steel targets are thicker than AR500 armor. That's going to matter. It also matters how they're mounted, as a free swinging plate or plate mounted against a very hard surface isn't going to behave (and be penetrated) the same as one that's supported by flesh/ballistic gelatin. No no no! Re-read the NIJ specs for hard armor please. Armor ratings ARE NOT INCLUSIVE. Please google Dr. Gary Roberts' work on hard armor testing. You'll learn a lot. Here's a start. More comprehensive and updated work can be found at LF. Plate material matters when it comes to what .223 threats will defeat it. As I've said before, polyethylene plates will stop M193, but tend to be defeated by M855 while AR500 plates will stop M855, but tend to be penetrated by higher velocity rounds such as M193. That said, there are many level III plates that will stop those non-spec threats and manufacturers often advetise them as "level III+" or "level III special threat." AR500 doesn't have a problem defeating M855.