There is several varaitions on a AL 391 and they can use different choke systems pending on the year and variation. Use the info below to help you idenitfy which choke you have. Or you can call Carlson's for assistance.
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Beretta/Benelli Choke Tube System Identification
Pic A) Standard Beretta/Benelli (Ber/Ben) Mobil Choke: - It can be identified by measuring flush mount choke tube. The flush mount chokes in this system are 2” long and have threads located at the muzzle end of the choke (top of choke where choke notches are.)
Pic B) Beretta Optima Plus/Benelli Crio Plus: Identified by measuring a flush mount choke tube. This choke system is 2-3/4” long & the threads begin 3/4” from the muzzle end of the choke. These two chokes have identical outside dimensions, however these chokes are based on two different bore diameters and should not be interchanged.
Pic C) Beretta Optima/Benelli Crio: - It can be identified by measuring a flush mount choke tube. It is 2-3/4” long and threads are located at the muzzle end of the choke (top of choke where choke notches are.) The Benelli Crio was in very few guns and is no longer being put into shotguns. Once again these two chokes have the same outside dimensions but are based on different bore diameters and should not be interchanged.
Pic D) Beretta Opitma HP: - It can be identified by measuring a flush mount choke tube. It is 2-3/4 long and the threads begin about a half-inch down from the top of the choke. This is a New choke system that you find in the A-400 Xplore shotguns.