Every shotgun barrel is indeed a law unto itself as far as patterning is concerned, and the only way to know what a given barrel and load will do is pattern it. Any number of things can influence the size and shape of shotgun patterns for better or worse, and two consecutive apparently identical barrels made from the same materials on the same machinery can pattern much differently.
Failing to hit the 'broad side of a barn' at 25 feet is a function of something besides choke, more than likely. Maybe the recoil of 3" maggie numb loads of buckshot had something to do with it perhaps? 8^) Shotguns often demonstrate a marked preference for a given shot size or brand or load, but at 25' you should be seeing some sort of defineable pattern out of almost anything, even if the patterns were wide open.
My usual range for patterning buckshot is 25 yards (75 feet). No real reason, it's arbitrary, but generally if you have good patterns at 25 yards you will have good patterns at shorter ranges also. No need in blowing great gaping holes in pattern paper at 5 yards or closer, no need to work the intervals with the pattern paper until you know what the load will do at the longest range at which I personally am apt to use buckshot. It saves ammo, noise and wear and tear on the shooter to start at long range, and then if the load looks promising to try it at 1,3,5,10, 15 and 20 yards to confirm the 25 yard pattern and get an idea of the size and shape of patterns at those ranges.
Remington is putting Improved Cylinder fixed chokes in most of its short smoothbore barrels these days. That little bit of choke (about .010" tighter than the nominal bore diameter of .729" in a 12 ga.) helps to make patterns more even and somewhat smaller, and I decided a good while ago to be happy with a fixed ImpCyl choke in a defensive shotgun. It saves money over going to the expense of having choke tubes installed or having Hans Vang do his thing. I do like to have forcing cones relieved a bit, that more than anything else I have experimented with seems to consistently improve buckshot patterns.
I am happy with a defensive shotgun barrel that will keep its pattern on a piece of notebook paper (8 1/2 X 11) at 25 yards, I will settle for 12- 14" patterns at that range. It happens I like tight buckshot patterns in defensive shotguns, some folks like 'em to be real scatterguns. It isn't for me to tell you what you should be looking for in your shotgun patterns. If you want wide open patterns, that's easy- just shoot S&B buckshot loads.
Right now several of the buckshot loads on the market (Hornady TAP FPD, Federal law enforcement loads and Premium sporting loads) are using a type of wad that helps control pattern size, and will offer good performance even out of a cylinder bore. I use Hornady TAP (red hull, 8 00 buck pellets at full velocity), there is a blue hull low recoil version and Federal offers low recoil law enforcement loads with the same wad if you'd rather use that.
Stay safe,
lpl/nc
