Over the years I've hunted with guys and gals who used everything from No. 7½ shot in 2¾" small game loads to 3" magnum shells loaded with No. 4 shot. Every upland game bird hunter has an opinion as to why his or her load is the best. I say, as long as you're happy with it, good for you. My personal favorite for pheasants is No. 5 shot in 2¾" magnum 12-gauge shells.
Over the past decade, the emphasis on improving shotshell performance for hunters has shifted to the area of velocity. Waterfowl hunters in particular were upset by the anemic performance of early steel shot loads, but some minds have been changed in recent years with the "high-velocity" steel loads rising to prominence and the shotgun shell boxes listing the feet-per-second (fps) performance of the shells therein. High-velocity shells are also available in other nontoxic types of shot, as well as lead, and requirements for nontoxic shot use on public lands is on the increase for all hunting seasons.
It is important to note that "high-velocity" and "magnum" are not interchangeable terms. When it comes to shotgun shells, magnum doesn't mean the same thing as it does when referencing centerfire rifle and pistol ammunition. Magnum shells contain heavier pellet payloads but sacrifice the speed at which those pellets travel. High-velocity shells may use a lighter shot payload, but they drive that payload out of the barrel at a faster speed than regular or magnum loads. The improvement in performance from high-velocity steel shot versus "normal" steel loads is something many hunters I've spoken to swear by. I switched to high-velocity steel a couple of years ago and took more ducks than I had in any previous season. What's more, with an increasing amount of public hunting lands demanding the use of non-toxic shot alternatives to lead, I've used these same high-velocity steel loads very effectively on other upland game – especially pheasants.
High-velocity loads deliver the payload to the target more quickly than conventional loads, but at ranges beyond 35-40 yards, the amount of additional energy each pellet delivers to a target isn't much more than conventional loads, according to articles I've researched that were written by professional ammo experts. That's because forces of deceleration working on the individual pellets seem to come together around those ranges when comparing high-velocity and standard loads. This may sound contradictory, but the faster the shot leaves the barrel, the faster is slows down until a point is reached (35-40 yards) where there is little added benefit to shooting high-velocity shells. This would lead one to conclude that for targets inside 35 yards, high-velocity loads will indeed increase the lethality of the shell and cut down on the amount of target lead by getting the goods to the game faster. The downside is that high-velocity loads kick harder, can create a flinch factor in high-volume shooting situations, and may sacrifice the pellet count of other loads to attain the velocities advertised while remaining within the safe pressure limits.
Shooters can enhance their downrange energy by going to a smaller (in shot talk that's bigger) shot size. A No. 4 shot pellet leaving the barrel at 1,400 fps has more ft.-lbs. of energy (killing power) at 40 yards than a No. 6 pellet moving at the same velocity. But again, by reducing the shot size, you diminish the number of pellets heading downrange and by the time the pattern reaches 40 yards, there will be fewer pellets in the kill zone than there would be if smaller shot were used. So where does all this get us?
High-velocity shotgun shell loads will serve you best if you're a waterfowler using steel shot or an upland game bird hunter who knows most of your shots will be inside 40 yards. Beyond 40 yards the increased price of high-velocity loads may not be worth it.
Magnum lead loads are good for hunters that want a denser pattern downrange but don't mind that it takes a split second longer to get there. Remember, magnum, in shotgun terms, means a heavier pellet load and theoretically a greater hit probability.
High-velocity super magnums, a hybrid of these two concepts in ammunition loading, work best for those who desire shoulder surgery after attempting to bring down aircraft. Just kidding. I know guys who use them on geese and get their limit. Then they go home and ice their shoulders.
The bottom line is to find loads you can safely and comfortably shoot, and then practice and stick with it. No amount of powder or shot moving down the barrel can substitute for good form and for the skill that comes with consistent trips to the range.