Wow, screw chokes that won't work with steel shot? What kind of an outfit would have manufactured such a thing in this day and age? Oh yeah, I forgot you said it was a Mossberg. Guess that explains it.

Call up and ask the manufacturer. Many choke manufacturers make multiple chokes in the 'same' constriction for different 'ingredients.' My Undertaker for example is specified for Heavi-Shot however H.S. makes an Undertaker specified for lead/copper-plate. I've found that my Heavi-Shot specified choke WILL shoot lead, but the lead specified Undertaker is NOT recommended for Heavi-Shot.
Hope this helps-

T .
heavi-shot markets turkey chokes specifically for their shot look them up on the web. i am not sure if they are extra full like the ones you got but the 40 yard patterns were very good on their web page

Ontario alot of Remington chokes are the same way. if you want to shoot heavy shot you have to buy another choke 90% of the time!

I agree with Honker that it is BS! don't doubt what you are saying tho

elmer
i dont think you understand just how tightly choked an extra full choke is. you just cant compress steel shot that tight together without @%#&ing your choke ,gun, or face up. they are really only for turkey hunting any way compare one to a regular full choke next time your in a gun shop you'll see what we mean .