patternmaster claims to catch the wad stopping it from overtaking the shot and messing up the load trajectory. I have one on my 11-87 and replaced my modified choke. The I.D. is larger than the modified, and the O.D. is exactly the same as the barrel. I dont believe it will tighten the shot like a traditional choke.
I was using the modified for 00 buck, and rifled slug (in a smooth bore). Other than the blast being diverted rear of the muzzle, I don't see any difference with the slug, of course. I thought it might shave some lead, but the cup just passes thru.
I have deemed this my all purpose hunting weapon in shotgun county. If I was
to designate a slugger, it would still go to my Ithaca model 37 with the deerslayer barrel. Got it in 1972, thanks mom.