Significant? Not really. If you compare apples to apples there is a potential advantage in that there would be more shot being expelled out the muzzle. In the real world you need to compare apples to oranges. Read the amount of shot contained in each shell from one manufacturer to another. You'll find some 2 3/4 inch shells that have as much, or sometimes more, shot in each shell than that found in another brand of 3 inch shell. If you want more shot coming out the muzzle you need to see how much shot is in the shells you are buying. All things being equal, you can get more shot into a 3 inch case than a 2 3/4 inch case. One other thing, depending on what you are going to shoot, OO buckshot isn't always the best. Sometimes #4 in a 3 inch shell is better due to the number of pellets/balls being discharged and the pattern density at the distance you expect to be shooting.