swamprat, please send pictures to model21shotgun@yahoo.com . Please list all specifications including weight and actual constrictions if you have measured them. I will include on my website.
I recently sold my 32" M21 'Duck'. They are great guns for 50yd shots on geese with Kent TM #1 if choked FULL/FULL.
Your 16 gauge 3" is the interesting one because I have not encountered one before. Thanks for the information.-Dick