Wanting on OEM collapsible stock/pistol grip. I own a Benelli M4 H2O model with the following mods using USA parts: 7rd titanium magazine tube, SS Mag follower, replacement front hand guards (look exactly like OEM), trigger, hammer, disconnecter.
He has published a host of informative YouTube videos. The web store, Freedom Fighter Tactical, is a great source of parts and knowledge. Some part, such as the collapsible stock are virtually “unobtainium” right now. There numerous methods to make these modification and stay in 922r compliance, although it is expensive. It a person want to modify the firearm to increase its magazine capacity or add a collapsible stock, then Federal Regulation, nicknamed 922r, comes into play. Being foreign made, it can hold no more than 5 rd in magazine and may not have a collapsable stock (military and LE excepted). Once broken in, it is a very reliable firearm with a 20 year history of successful military service, although it is expensive and heavy. The Benelli M4 is a pistol driven, semi auto, 12 GA shotgun made in Italy.