BBF, Interesting, it seems to me that if the outer diameter of the barrel appears to be about 1/8th inch "lower" in the receiver than the Ultra slug barrel then the firing pin would be about half that or 1/16th inch lower (offset). If it is it might still fire the primer and if it does (either centered or offset a bit) the shell is still centered in the bore so there is no danger after the primer goes off. :oops: :oops: :oops: Brain cramp!!! If the barrel appears to sit 1/8 inch lower in the receiver and is "bottomed out" in the receiver then the firing pin should be offset (lower) by the same 1/8th inch, perhaps making it impossible for the firing pin to strike the primer. :oops: :oops: :oops: . The worst that could happen would be a broken firing pin. I say if you want to try a primed shell or even a loaded one go for it. You might want to try a fired shell in it first and then check it to see if there is another firing pin strike evident and where it is on the shell. If that 16 gauge barrel works on your 10 gauge receiver then all others (12,20,28 and .410) will work also since the others all all of the same outer diameter....<><.... :grin: