depending on the shotgun..the Oring may be surplus to requirements.... the one I got made up sits snugly in all my shotguns now except will now be loose in the astra cyclope in USED to live in and its too fat for top barrel in the U/O bakail....If I wanted to use in the astra again one or two layers of insulation tape would center it nicely.it was so snug in astra before if I oiled it..wouldnt fit in!!! turned it down just a smidgen.