My gun (mx8 vintage 1977) is at the gunsmith right now but I think that is what I have as well(briley series 2 thin wall flush chokes) . I have f,M,LM, and I think the other two are s-1 and s-2. In any case I'd like to swap one of the 'S' chokes for a IM. The side of the choke clearly maked Briley, brown imprint color.
Larry 208 773 8804