To get the tightest patterns with Buck shot, or even large size birdshot( #4, #3, #2, #1)A cylinder bore gun will produce tighter groups if you use a fine filler, like Jiffy Brand Corn Meal Mix( less than 50 cents a box at your grocery store.) You load the powder charge, then put in whatever OP wads you intend to use, then the about half the amount of corn meal Mix, then the shot, bounce the barrel up and down to settle the buckshot into the mix, and then pour the rest of the mix down the barrel, and bounce or shake the barrel up and down a bit to settle the rest of the filler in and around the pellets. Then top off with an Over shot card or two.
( Obviously, you will need to determine how much filler is needed for any given load of buckshot, as the amount of filler depends on the size, number of pellets, and the total weigh or pellet count of the load. I have some glass vials from some cigars I bought years ago, that I use to replicate, within reason, the cubic dimensions of a shotgun barrel or cartridge, to figure out how much filler is needed in a given load. )
You can also put the pellets in a Paper cartridge you make by taking strips of newspaper, turn them around a stick( mandrill) that easily fits down the muzzle, but not too loose, twisting one end of the paper to form the base of the "cartridge". Then put the shot and filler in the cartridge, and twist the top to seal the package. You can then run the whole package of shot down the barrel and the need for an Over shot card disappears. The paper will protect the bore of your gun from leading streaks, caused by the pellets rubbing against the bore when the load is fired. The fine filler will keep the balls from distorting, so that they fly together Longer, making for smaller patterns at ranges out to 30 yds, and sometimes further. The balls are heavy enough to break out of the paper package, without you tearing off the top of the " cartridge" as you load it down the barrel.
You will have to experiment a bit with these shot packages, determining how many times you wrap paper around the mandrill to make a solid tube that will stand up to the shot. 3X around worked for my 12 gauge, but it might only need 2x on your gun. It often depends on what kind of paper you use, and how thick or strong it is. Newsprint is a commonly available source of paper, of a known thickness and strength. Because its available so cheaply, I recommend its use! :surrender:
Some shooters report good result by pushing the package of shot into the muzzle, and then tearing the top of the paper off, and using an OS card or two to hold the entire load in the barrel. All you can do is try it both ways and see what kind of results you get with YOUR GUN.
With buckshot, You don't need heavy powder charges. Stick with loads of 3 drams( 83 grains by weight) or less. I find using 2 3/4 drams( 76 grains) produces fine patterns out of my gun. The heavy buckshot is going to penetrate further on any game at ranges out to 40 yds. By 50 yds, they may still hit the target, but they have lost a lot of their velocity, and " punch". Oh, I won't volunteer to let you shoot at me at that distance with a buckshot load, but hitting, and killing deer at that kind of range with buckshot are two different matters. Most hunters who use buckshot on deer find they are shooting small deer at less than 25 yds., classically running shots, through brushy bottoms.
I am hoping that you are planning a Coyote hunt with these loads, as they make very good medicine on Coyotes, provided you can get close enough- either by calling them, or ambushing them.
Best of luck to you.