MGM is one of (if not "the") the largest manufacturers of steel targets...
From their website, the caps and bold print are theirs...
PLEASE NOTE: DO NOT SHOOT STEEL TARGETS WITH 'XM-193' AMMUNITION. SUCH AMMUNITION IS INTENDED TO PENETRATE STEEL AND WILL CAUSE SEVERE DAMAGE TO TARGETS, INCREASING THE LIKELYHOOD OF FAILURE AND PERSONAL INJURY. DAMAGE TO TARGETS RESULTING FROM THE USE OF 'XM-193' WILL NOT BE COVERED BY THE WARRANTY.
So, it would stand to reason that if the measly little .223 with a steel core can do damage, a high-powered round like the 54R certainly would.
I have both 1/2" and 5/8" AR500 plates we take to the range...thousands of rounds, including a bunch of 54R (match handloads) and not so much as a ding, but we're shooting at a much greater distance (565). They've taken 50 BMG hits with no problems at that range.
Any steel at 200 can be an issue with high-power rounds. Targets should be free-swinging, and hung from the back side of the steel so they naturally angle downwards- deflecting the frags into the dirt.
I know guys shoot mild steel all the time at distances that close (200), but I wouldn't. Once mild steel (or shot-out or abused AR500) gets so much as cratered it is unsafe as it is impossible to control the direction of the fragmentation. If you're going to shoot steel core, high power rounds at that close a distance, use a soft target...