I have a few plow discs scattered at various distance. I'll drive away from them till I get around 13 hundred yards from the farthest. With multiple discs scattered at ranges from 13 hundred + to around 500 yards, it makes for fun and useful practice. Plow discs are not soft steel. You can wear them with a anything up to a 300 RUM so long as you don't bring them closer than about 500 yards. Shoot them closer than about 450 yards with guns that big and they will eventually start to get little cratters and cracks and then holes in them. There are different size discs with different thicknesses. The ones I shoot are all fairly close to 18 inches from side to side. That's pretty big for up close lol but about right for around 1000 yards. 18" is big enough at 1000 to hit with a minor mistake in wind or personal mistake. I consintrate on trying to knock my bolt out of the center that fills the hole instead of the hole thing. This seems to make a better marksmen out of me rather than just settling for hits all over the disc.
I paint my discs white with spray paint. I then paint a + symbol in bright orange in the center so as to give me a good visible center mark at those longer distances. A hit will show up very well in the scope. When I change distance of before pulling out another rifle I just drive down to the targerts and touch them up with a little paint to cover up the impact marks.
I use a couple 12" blind flanges which measures 19 or 20in depending on the #rating of the flange (150# or 300#). They are mild steel, however, at 2" thick, even the 300 & 338 RUMS don't do much in the way of damage. Here are two pics thru the Optics, top pic is @ 550yds thru a Leupy VH reticle @ 25x, Bottom is same target @ 1060 thru NF NP-R2 22x.