Yes I have a ring in place of the standard bead and it is a dinky little sight.
I used it in conjunction with an aperture sight in a vintage shoot once and as it was a bright day, I could almost choose which part of the kill I could place the pellet. In fact, I felt the sight gave me such an advantage over others that I have never competed with it since. Having just a shadowy ring around your intended point of impact works really well and I'll have to take her out again for a shoot one of these days.
John
Currently looking for Baikal Makarov pistols with the following prefixes to the serial number: 98, T01, T09, T21, T22
Prefer boxed or cased but will consider loose examples too.