He is very right, read my post....
it look like a semi-auto 1100 or 11-87 !!!!
The hole you see on top of the rear handle is the nut that hold the rear handle, you loosen or tighten it with the little chant that is in front of the forearm...
I'm wrong. Apologies. Made worse because I recently owned a Benelli M4 with the ( more or less ) same action including the recoil spring down the telescoping stock.