Go to your well stocked outfitter and buy $100 worth of various buckshots and an open mind. . I did a fairly extensive patterning of my last new "shotgun" a Mossberg Shockwave 590. Now this has a cylinder bore yes I know, however it took me back to the basics for a minute. I experimented with 2¾" and 3" 4B, 1B, OB, OOB, OOOB and some boutique loadings.
I found I got the fullest patterns from 3" Winchester 1B and 3" Federal Premium OOOB from 7 yards to 30 yards. I found velocity is everything with patterning before constriction becomes a factor. Keeping the wad or shot cup from blowing the center out of the pattern is the key.
If you're going to constrict the shot column, the smaller the shot, the more constriction it will tolerate until patterns poorly. Wad retarding devices like the Patternmaster work really well with loads in shot cups. I have had good luck with standard loadings of 9 pellet OOB 2¾". The shorter the shell the better the pattern. I have one barrel zeroed for 90 yards with a specific load with the choke tube.
For conventional constriction chokes, I liked the 3½" OOB with a flush mounted Extra Full. It did very well with a 28" barrel. One shot kills on open field whitetails out to 70-80 yards is commonplace. I have experimented with backbored and conventional diameter barrels. I am of the opinion that the loss of slug capabilities is not worth the recoil reduction of the backboring and I noticed no remarkable pattern improvement.
My current favorite buckshot load is the Tactical #1B Flite Control. Very tight pattern out to about 30 yards fired from 14" cylinder bore. Flite Control Wad has regarding fins that slow the shot cup to keep it from blowing through the pattern. Hornady attempted to copy Federal with this and their design is not as effective. I have not yet tested this load with choke tubes, but it is to be used with constriction chokes and not wad retarding devices per manufacturer.
I am also convinced that #1B is better than either OOB or OOOB for pattern and penetration. However there are not as many loads available and the Federal loading are not true .30 which leads me to believe that they are using the same pellets for their 12 gauge #1B as their 20 gauge #2B.
Apologies for the long post.