i have a poly choke adjustable on mine
Poly - Choke II for Saiga 12 [S12polychokeii] - $99.95 : Mississippi Auto Arms, Inc ::, Your Source for Saiga, AK47, AR15, Tromix, Glock, and SKS firearms and accessories
it screws on to the threads already on the barrel and works great.
it was a little difficult to thread all the way on but i guess that means it won't be falling off anytime soon.
totally adjustable for tight patterns out to slugs
not sure if that was what you were looking for but there ya go