which one rocked that gong the hardest?
on paper, with factory offerings, hornady supplies the following info at 200 yds
450 : 20" test barrel, 250 FTX - 1289 ft/lbs (1524 fps)
243 : 95gr sst - 1478 ft/lbs (2648 fps) (barrel length not specified in hornady.com data, other loads wehre length is shown for the 243 all show 24" barrel)
204 : 26" test barrel, 32gr vmax - 699 ft/lbs (3137 fps)
so at that distance the 243 carries the most energy, however the only round above the 3000 FPS impact threshold of ar 500 is the 204 ruger. at 2648 fps that SST should have splashed and just scratched the paint. my ar in 204 will splash with that load at 200 yds on AR500, but i'm only getting 4000 FPS mv, not 4225 that hornady gets from their 26" barrel.
just so you know, shooting mild steel like that can be dangerous. once it starts to dimple - you can actually get frags coming back at you in a ricochet.
on hardened steel, the bullet just "splashes" and comes apart on impact.
just for safety's sake - make sure you dont shoot that plate again, especailly if you're doing close range work with a pistol.
just a little education on steel
https://www.youtube.com/watch?v=Lc64gdz67u0good ar500 steel can be had rather affordably. i've got a couple 12" gongs that i acquired for less than $40, however i had to make my own target stands and provide mounting hardware. its definitely not something i'd want to outfit an entire range with at once, but a target here and a target there, and soon enough you'll have a steel festival to shoot at. i watch for blems and sales and build my own target stands using chain and grade 6 carriage bolts for mounting.
hth