Re: 190 SXR vs 1/4" steel plate @ 1/2 mile
hardness of the steel is far more important than thickness. While both is needed, in the long run a mild steel plate will get really chewed up, and can make spotting exactly where your hit landed hard, because sharpnel from the bullet knock paint off all over the place.
AR400 will work for long range, but AR500 is best, 3/8" AR500 will take just about anything 200yards and out. I've shot a 6x6" plate of AR500 (free hanging) at 200yards with a 6.5mm 140 VLD at 3385fps MV and just given it the SLIGHTEST dimple, we're talking <1/32"...
"Out of range" is a theoretical concept as far as I'm concerned. Send it!