Pete,
From a pair of official NRA Bullseye target faces in my garage:
X ring: 1 11/16" diameter
10 ring: 3 3/8"
9 ring: 5 1/2"
8 ring: 8"
7 ring: 11"
All scoring rings are same diameter at both 25 and 50 yds BUT 8-9-10 rings were black on the 50 yd target while only the 9-10 rings were black on the 25 yd target.
Good shooting and be safe.
LB