I bought a six pack of these heads off ebay just to try out. The guidelines say that I should use the UBAR however for these heads since I' m shooting carbons. I haven' t been able to find them on-line, but on the NAP websight, all they look like is a rubber o-ring. Is this all they are? Could I just use any o-ring that would fit in there, or should I stick with the actual UBAR' s from NAP?

Any suggestions? If I need to use those specific kinds, is there a place on-line that I can order them?