“Ideal” in your scenario is going to be a pretty subjective. Dogs vary highly as to type, ability, and training. Then there’s the cover — death march CRP, chest high, with a bird flushing up your nose, or a clean cornfield inclining birds to sprint a 100 yds or further and get up a quarter mile away.
As BK, and Battue mentioned, don’t dither over chokes because ranges will vary from bird to bird and shot to shot. IC, LM, HM, and F will all work. I also don’t see any use in loading different shot sizes in doubles or pumps or SA’s assuming a first closer shot than the second. I’ve never been clever-fast at the correct barrel selector-safety choice on doubles to account for different range birds and the bigger or smaller shot. I load the same shot shells in both barrels or magazine.
So, no ideal choke. Most will pick size 4,5, or 6 shot for big roosters. I usually go with 5’s but probably mostly 6’s.
As to shotguns, I’ve used the 28, 20, 16’s and 12’s. I’ve killed a few with a H&R single shot 410 to see if I could. By far a M choke was the most often used. Now, the biggest factor for me is the shotgun. Notably weight. Handling qualities, reliability and quality all follow. I have no use for a pheasant shotgun weighing much over 7lbs. 7 would be max for a 12 for me if it was superlative in all other areas. Make that 6 1/2 lbs for a 16; 6lbs max for a 20 and under that for a 28. 26-28” barrels are more the norm although I’ve used 24” barrels with no problems.
Weight often becomes the issue when smaller gauges are built on the same frames used for larger gauges which is a common economic maneuver for all makers of all action types. Until you get into higher dollar guns. Many folks don’t seem to care as much about this as I do now.
When I was a junior (1969) in college, we had a particular snowy year in Iowa. My buddy and and his two GSH’s cut too many classes that fall and our Government Acres (called CRP now) were loaded with birds. I alternated between a clunky Savage 311 20 (M/F) and a Rem 870 12 gauge (M). With legal daily limits and possession limits, I killed about 90 wild birds that year and my bud killed just over a hundred. I even wrote my biology term later on the plant and animal content of their stomach contents. Of course, understandably, this required a lot of field work..
Both those guns worked fine though Im a bit more choosy now. Anyway, that’s the present view from here.
