USBR Ring Size:
10 0.100"
9 0.300"
8 0.550"
7 0.850"
6 1.200"
5 1.600"
4 2.050"
The largest group that would score 250 0X on the USBR target would be 0.224" + 0.100" = 0.324". A 2500's smallest group is 0.276".
Outside of perfect targets, it's hard to translate an arbitrary score from one...