Stallones,
Remember that patterns all follow a Rayleigh distribution (very similar to the normal/bell curve distribution), the classic rifle/artillary/bombing dispersion distribution.
Let's say that we are dealing with 80% patterns as baselines for 1 oz, 7/8 oz, and 3/4 oz loads. If hard shot is used, such pattern percentages are extremely common, especially from full-choked barrels. All chokes with all shot loads and shot sizes will throw 80% (within a 30" circle) patterns at some range. Keep in mind that the heavier the shot load the more pieces of shot in that 80% pattern.
0ne-ounce loads that generate 80% patterns will, theoretically, place exactly the same number of pellets in a 30-inch circle at 40 yards as a 1 1/8-ounce load that generates 71%. Note that a smaller percentage implies a larger pattern diameter, which allows more aiming error angle. Empirical results tend to be consistent with this estimate. A long-yardage handicap target generally stands very little chance in a 71% 1 1/8 oz's pattern, unless the pattern is extremely "patchy" or "holey". Exactly the same claim can, therefor, be made for the patterns thrown by good-quality 1 oz loads, even when "large" (for target loads) shot is used. In fact, it is not at all uncommon for 1 oz loads to "throw" 7 1/2 shot even better than all but the best 1 1/8 os loads (possibly due to less shot deformation and/or shorter shotstrings?). Relative advantages to the 1 1/8 oz loads: More shot (than perhaps necessary) and a (false?) sense of security for shooters who remain convinced that they need "all those soldiers". Relative disadvantages to the 1 1/8 oz loads: More expense, more noise and recoil, with their negative effects on the shooter, and more difficulty obtaining pattern per centages that are equivalent to those which are more easily obtained with lighter shot charges.
Similarly, 80% patterns of 7/8 oz loads and 3/4 oz loads theoretically will yield patterns that are equivalent to approximately 62% and 60% of 1 1/8 oz loads, respectively. See note above on lower % pattern diameter. Again, empirical results tend to support such estimates. Such "modified choke" patterns can reach out a long way. International trap shooters, who shoot 24 gram loads, routinely break targets on second barrel shots that are taken at ranges that are pretty close to those of 27 yard line handicap trap shots. At the very least, these "mini loads" ought to be more than adequate for all but the most demanding 16-yard and doubles shots, and this would be true even before the loads were "tricked up" using lighter shot and faster velocities. The "advantages" of 1 1/8-oz loads are beginning to look pretty small, aren't they?
Oh, about "smaller patterns"; maybe not, at least as a general rule. Over 20 years ago, Don Zutz demonstrated that, at least as often as not, there are next to no differences in the diameters of modified choke and full choke patterns at 40 yards. It takes statistical analysis to really see the difference in effective diameter of similar patterns. Full and modified patterns are identical in distribution and diameters with a difference of about 5 - 10 yards. The main differences have to do with the number of pellets in the pattern, especially in the patterns' "cores". There really is not "core" to a pattern; shot per square inch increases according to the Rayleigh distribution in an orderly, analog fashion. It would seem that the need for "more accurate aiming" might be located more often between shooters' ears than it is out where the targets fly. Depending on the difference between shot sizes and loads, chokes, and ranges, the allowable aiming error difference can be small or large.
