I have a 20 gauge 1100 s/n R123182K (Nov,1990 ?) stamped on the receiver. One person at the factory said I could buy a barrel for 3" shells another said only if it was listed a a Magnum or any gun made after 1985. I thought this was made after but nobody there seemed to be able to give me a definite answer. Any suggestions?

Sorry...not sure about this question.

You would think the factory could give you a definitive answer...

"R" prefix in the serial number means it was made since 1990 and not November
"K" suffix in the serial number means your gun and receiver is a LW or LT with a 2 3/4" receiver and not designed or intended to shoot any 3" loads.
It can be converted, but will require more parts than just changing a barrel.

If you want to find out when your gun was made I will need the two letter barrel code found on the left side of the barrel near the receiver

If your serial number ended in "U" instead of "K" it would be a magnum receiver.
In addition to a 3" barrel you will need to change the action sleeve and possibly machine tweak a few places to make it function properly.
Once converted it will not shoot light loads unless you change it all back.

Excellent job with the member question TuJays !!

+1 reppoint for you sir...

Thank you, but we don't know if he has read it yet:)