Slugs in a 12g BRNO O/U barrel

[Pete04]

I have a BRNO zh 104 7x57R over a (I think choked) 12ga x 2 3/4"
Is there a way to determine the choke of a shotgun barrel? And can I shoot 12g slugs with it.
The reason I think it is choked is when I push a mop from the breach it gets harder to push at the muzzle.
Thanks

 

[zywina]

When I bought my BRNO 307 series combo gun 22hornet/12ga., it expressly says no slugs threw the shot barrel as it may cause damage. I have never miked my extra set of 12/12 barrels for this gun, but I would take it to a competent gunsmith before ruining a good set of barrells for your BRNO 104 series, Dale Z!