Did not fit my gun. - Trulock Boar Blaster Choke Tube

I purchased this Trulock Boar Buster extended choke tube to use with buckshot in my Hatsan PS turkey shotgun (12 ga.) My research indicated that Rem./Choke choke tubes were the proper match for my gun. Unfortunately, while I like the look, design and quality of this tube, it does not fit my barrel. The threads measure (.808) BUT the shoulder is (.818) ...The extended turkey choke(V3)that came with my gun threads measures (.808 same as above) and the shoulder is (.812) Is this problem perhaps a quality control issue or is the Rem/choke just an incorrect match for my gun? The bottom line is that I am looking for an extended choke tube to use with buckshot, preferably the Boar Blaster with the compatibility of my V3 choke that came with my gun.Your help is truly appreciated. Thank you, Gerry V.