Have not received it yet, but hope to buy a few O rings for my 11-87. Thanks for the info. Are you looking to make a semi-auto lookalike of the 7188? I know that there was a semiauto prototype called the 7180. I have hoped to make such a set up myself, but I am reluctant to take off the front sight (rifle type) and have it put on a bayonet adapter (available from Scattergun Technologies) or have a set of ghost ring sights installed that would be inaccurate to the original specs.