Do a search. There is an entire thread in hoppe ring educate multiple pages
I know the original Rambo's and Hoppe's had the ivory ring right around a 1/4 inch., maybe a little longer, maybe a little shorter. At any rate, the black butt cap was a little shorter than the ivory. There was no bumper but he never used phenolic on the end either. Phenolic chips pretty easily where as the material that he used was more like a real hard rubber or a linoleum material that took more abuse without chipping as easily.
Dick