RE: Buckshot & Choke Choice?
Goodfella, I have hunted with shotguns and buckshot for more than 20 years now, and I have a few possibly worthless opinions. Here goes...
As timbercruiser said, you will need to pattern your gun with different brands and sizes to see what it likes best. My 870 and 1187 shoot Winchester 3" 00 best, but my old Browning liked Remington 3" 000 better. As to buying an expensive choke, I would not recommend it. If your season is only 6 days per year it is probably not worth it. Where I hunt the season runs for 4.5 months, so we can invest a little more without feeling foolish if we don't get a deer in a week or two. I have found that the standard "modified" choke works just about as good as the expensive ones, especially if you are trying to stretch your budget.
Personally, I would not recommend #4 buck. The pellets are really small, and they do not carry energy as far as the larger pellets. Instead of using smaller pellets, I would advise going to a skeet or trap range and shooting several rounds to improve your skills. It will not take much to make you a better shooter, and you will see the results the next time you pull the trigger on that 870 at a nice deer.
P.S. Don't waste your time trying a turkey choke with buckshot. The extra-tight constriction actually makes the pellets fly wild instead of patterning the way you want them to. Usually modified or full will work best. Good Luck!