1/4" will likely be fine for 300 yds. But at 100 yards, the 3/8" AR500 targets I have get absolute destroyed by fast 300 mag bullets. They look like hammered metal. There are some holes in one of my 3/8" AR500 targets but I can't remember if it's from a 150gr 300 mag or my 375 H&H, either way at 100 yards.
