The only gun I recall shooting any 3" 20's (1 1/4oz) from was a Richland 707, which with 28" barrels weighed in at 6 lbs. It was bearable for a few shots but not truly comfortable. My feelings are if you need an ounce & a quarter of shot why not shoot a 12. If you need an ounce why not shoot at least a 20 or better yet a light 16.
I did take a some of those fired 3" 20's & reload them with 1 1/8 oz of #5's. On the few occasions when I carried a shotgun to the squirrel woods they were poison on the bushy tails, but no more so than a 16 would have been with the same load.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra