As with all shotguns," range " has to do more with the size of the shot chosen( Pellet energy retained) and whether your barrel is choked. There is a difference between maximum range( physically) and "Maximum Effective Range".
All Cylinder bore guns are generall considered to have a maximum effective range for birds of 25 yards. Improved cylinder choked guns are effective to 30 yds; Modified Choked guns are effective to 35 yards, and Full Choked guns are effective out to 40 yards. These are General Rules, because to be effective at killing birds, The SHOT PATTERN must be dense enough to put enough pellets into the birds at these ranges.
The use of plastic Shotcups in modern ammunition has realistically probably extended the ranges of all Smoothbores about 5-10 yards, depending on the shot size used, and the velocity of the load. The Shotcups not only protect the lead pellets from being deformed by scraping flat sides on the outside pellets that contact the bore, but hold the shot together for some small distance outside the muzzle of the barrel, before the shot is fully affected by the air after it releases from the lighter cup.
You can use the " Time of flight" tables in the Lyman Shotshell Reloading manual( any edition) and a calculator to determine just how little the delay needs to be in releasing the shot to see how effective range is extended by plastic cups.
For a cylinder Bore Smoothbore, we can either use plastic cups, ( Necessary for non-toxic shot) or make paper shotcups that are designed to delay the release of the shot.
You can also add a few extra yards by using a larger shot size. I use #5 shot, for instance, in my cylinder bore shotgun, rather than #6 shot in my modern shotgun that is choked, to achieve a longer effective range with my MLer. I also increase the weight of the shot charged used, to add more pellets to the patterns. a MLing shotgun give you that flexibility in loading that you don't have with shotgun casings.
All this involves testing, with a given gun, and components, varying the amount of shot, or choice of shot size, and seeing how such loads pattern at various ranges. I have spent so much time shooting short targets with pistols and rifles at 25 yds. that all I need to do is close my eyes, and I can pace off the distance to within a yard. For that reason, my ability to estimate range accurately is much better than most people's abilities. I am within 2 yards pacing off 50 yards, too. I grew up in a suburban neighborhood that had 50 foot lots, so all I have to do to see " 100 yds" in my mind, is to remember looking from my parent's home to the house at the end of the block- 6 lots away.
The point is, that you need to do your testing, first on a range, where you know the measured distances, and then in a field, where at most, you only put out ranging stakes. ( Do this for hunting turkey to let you know exactly when the turkey is within range of your pattern. ) Don't hesitate to take a tape ruler out into the field with you to help you set your ranging stakes. I do this when deer hunting from a tree stand, early before the season, when I trim brush away from my shooting lanes, and set up the stand. The ranging may be just a new blaze on a tree, once I am sure of the distance. If hunting open fields, of course, you will need to take along some wooden stakes to place out in the cover( but not in the middle of any game trail.)
