In my humble opinion, the Sgt. Peep is a wonderful addition to the 1902 sight, which is my favorite of the Krag rear sights.  The peep is approximately 0.04 in diameter, which is painfully small considering the relief from ones eye.  However, per CMP rules, you can enlarge this peep for competition use.  You can go about 0.07 before you're in danger of running out of metal to drill... but that makes a world of difference!!!  I've actually built my plate up slightly using JB Weld, and enlarged to 0.1 for match shooting.  This gives me an excellent sight picture!