I concur-- I use AA 12 Trap loads- both Lites and handicap for the second barrel- I have shot hundreds of both pheasants and pigeons- in theloaded and remote control released spring traps for retriever trials- also Tower released phesant and barn pigeons- and within proper range the 12 1 & 1/8 loads will kill them in flight-
Glad you specified the species here, however.I am 70- no Tom Roster or the late Bob Brister- BUT- IMO and IMO only- incoming and overhead pheasants in flight are the easier of the shot opportunities to kill deadly and clean in flight- birds flushing and going straight-away are the hardest, and there, a heavier load in the second barrel may well be needed to get clean kills- and not leave cripples for the predator patrols--
Here's another observation, for what it is worth- One man, or perhaps two men hunting together but taking "round Robin" turns with a single close working pointing dog- they ealk in on the point and kick and scuff- 75% (est'd) of the time they'll get a low and straight away bird- hardest to kill- a straight away climbing bird, if your lead and swing are correct, you'll get the pattern in the head and neck-dead bird right now-
But, make that a flushing dog, and especially on a day with gusty winds that change directions- and you'll usually see more birds that flush and climb in that corkscrew pattern that resembles a UH-1 Huey with a loose Jesus nut- the rotor spin is erratic--
Pick the double (or model 12) and choke and barrel length you like best- but for pheasants- make mine a 12 gauge- a great game bird like John Q. Ringneck deserves no less afield- a strong flush, a cackle that sounds like a cathouse madam imitating Yoko Ono, a spirit that will gladly spit vinegar in your eye if he could, and a game bird in his own right that does NOT surrender his life easily- what a great challenge!!