wow...who would ahve thought there are so many options and choices...just to go hunt some bunnies n squirrels lol. seems to be the average is #4-6 so maybe ill split the difference and go with #5
What you need to do is to try these various sizes in your gun and see what works best on paper putting a good number of pellets in the center of the target. I have a caplock 20 bore SxS that loves #7½, and knocks down squirrels and pheasant and grouse, but for some reason doesn't pattern well at all with #6.
I have a flintlock 20 bore that hates #7½, and does much better with #6 and #5 shot.
You have to remember as the size number of the shot goes down... so does the number of pellets if you are using the same measure. So in your 24 bore 3/4 of an ounce of #5 is a lot fewer pellets (126 pellets) than when you use 3/4 of an ounce of #7½ (254 pellets), but the pellets retain killing momentum at a longer distance than the #7½.
A good "backyard" testing method is first to pattern the load, then take an empty steel, tuna can, and place it end-on at the distance that you plan to shoot. Shoot the can and see if any of the pellets striking the can failed to penetrate. In a good load, nearly all or all should go through.
#8.......averages 399 pellets per ounce
#7½....averages 338 pellets per ounce
#7.......averages 291 pellets per ounce
#6.......averages 218 pellets per ounce
#5.......averages 168 pellets per ounce
#4.......averages 132 pellets per ounce
So the #5 gives you about 1/2 the amount of pellets as the #7½, but each pellet is individually heavier.
LD