12 or 16mm Biz 400, 16 will stand up to my 416B unless you are being a Dick.
My big plates are ex dozer blade about 12-13m & as hard as, they "ring" well :D
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This is what Greg's 338 does to 20mm mild plate @500yds.
http://i579.photobucket.com/albums/s...m/PC020373.jpg
Your dozer plates are 500 and if you could test both sides you would probably find the concave side that has been work hardened is up well over 500 brinell. hence the ring:D Got a couple of bits of what im fairly sure is NIhard for you to test Greg,just got to figure out how to cut it! might have to arc air it
Rang two places up here in akl to get some 400x400x16mm plates made $52 each! Is that expensive? I have a few more places to try, but It would be good to know what's a fair price in your neck of the woods.
That was for mild steel 16mm plate. Biggest calibre we have is .308, so should be fine for a while?