after looking at a misc Saiga trunion (not sure of its oigin I noticed the lugs are wider apart than a saiga 410 and more like a 308 (its not bulged and has a 22mm bore) I can almost get a 28 guage shell through there as is. It would be alot of work to get this to work with a standard bolt
the bolt is almost going to need to be long like factory on a 410 to be able to get this to feed with a shroud.
also note how the factory bolt head is reduced in the extended section so it will fit between the upper and lower guides /shrouds and rotate. Im thinking a bolt head extension pinned in, might be the ticket like on a 20 guage. it might be the trick to get a 28 guage to work as well