Steiner used to make a light that is specific to the Benelli m4.
It’s called the mark7 . It replaces the magazine cap and is about 350 lumens.
It’s out of stock at most places. If you go to the Steiner website. You can sign up on the wait list. ( they’re selling it for 49 bucks directly. 200 bucks if you get it from a retailer )
My m4 right now uses a clamp on light (I use either a stream light or a surefire pistol light that is mounted on a quad rail )