it really has to do with muzzle energy on target. 50bmg is an example however shootsteel.com has these ratings for the min yardage on their 3/4" ar-500 steel.
50BMG ball and brass solids – 300 yards
50BMG AP and API – NOT RATED
416 and 408 lead core – 300 yards
416 and 408 brass solids – 400 yards
The rest of their ratings are here.
Our Targets
the lower line to 650 has been around for a while now. It closed briefly during the court case but opened up as soon as that got resolved.
In all honesty you won't find a better range with steel out to 1000 until you drive to Alderbrook in NH or Sheepdog in NY. I would even extend an offer to you to help coach you up on building dope and getting comfortable at distances beyond 300. They had a free course to do just that a few weeks ago and I think like 70 people came with 20+ coaches. Next month Rob Brantley from team manners / bushnell is hosting a 2 day there to work on PRS skills. Guy won king of the 2 mile and is an extremely skilled marksman.