Thanks all for your feedback. I haven't had a chance to get any paper patterning done with RST 16ga/2-1/2" regular shells and spreaders. Have to get in gear, our grouse season is almost here.
I used the word "rare" for 26-inch barrels because that's the word used by R W Elliott on page 126 of his definitive book
Uncle Dan Lefever Master Gunmaker.