I haven't done anything with 3" shells but I have been doing some experimenting with 2 3/4". I use Red Dot powder with a #30 MEC bushing with 6 shot. That is a little hot for Red Dot but it hasn't torn the pheasant up. The problem comes in when you get into quail. These loads will tear a quail up pretty bad so I try not to use them for anything smaller than pheasant. I don't know about your gun but my doesn't cycle 3" as fast so that might be something to take into consideration but good luck with what ever you decide.

I grew up in South Dakoata and have shot hundreds of pheasants by now. I would never shoot a 3" shell at them for the following reasons:
a) puts too much lead in the bird and they are difficult to eat
b)too much recoil, why knock yourself out for a measely pheasant
c) shells are too heavy to carry in the field
d)too expensive... wasting lead that is not required

I wouldn't shoot size 7 1/2 shot at them because:
a) I would not want to get all that shot in my teeth nor would I like to take the time to pick all those little pellets out of the meat
b) Range is limited to about 20 yards and most of our pheasants are hit at 30-40 yard range sometimes 60 yards
c) They don't knock pheasants down... they seem to be great for pen raised birds but the wild ones are tough and keep flying.

I shoot 2 3/4" hot field loads with size 4 shot. I wait until they are at a nice 30 yard range to shoot but can drop them effectively at 60 yards if necessary. Most pellets that hit them go clear through so I don't bite into them at dinner. The pellets are big enough to pick out of the meat if some remain. I like to hunt with guys who shoot 7 1/2s because I get to shoot most of their birds as well as mine.

I hunt pheasants in Illinois with the 3" 7 1/2 and I have killed about 15. That is also what the outfitter recommends too. If availiable try Fiocchi shells. They are more expensive, but they are geared primarily for wingshooters and they have a pheasant line.

3" #6 with an improved cylinder or modified choke. If the birds are close and also far, try a 4x6 by Remington. If you need faster ammo, go with Golden Pheasant ammunitioni by Fiocci (which is nickel-plated lead) I have tried the #7 1/2 Fiocco nickel-plated lead in 2 3/4" for pheasant, but felt the bird was closer than most. Try different brands and see what your gun likes most.