For a single RB load in a 12 gauge( nominally .729") smoothie, I would start with 3 drams( 83 grains) of 2Fg and go up from there in 5 grain increments to develop an accurate load. Don't plan on going much past 90 grains, as that ball is 1 1/4 oz. in weight, and it doesn't have to be leaving the muzzle at high velocity to kill about anything it hits( and passes on through).
Buck and Ball loads get a bit more difficult to judge. You are adding more weight to the Load you are shooting, and that will produce more recoil, as well as increase the pressure in the gun.
You can try 00 Buckshot( .33" in diameter, nominally) and that should allow you to put 3 pellets per layer in your bore. However, if your bore is truly ONLY .72 caliber, that is a bit small, and you many have to go down to 0 Buck( .32 caliber), to get 3 pellets to fit in one "layer" in your bore.
In police loads of cartridge 12 ga. shells shooting 00 buck, the casing would hold either 9 or 12 pellets, depending on whether the gun is chambered for the 2 3/4" shell, or the larger 3" shell, respectively.
But, you are wanting to put a Single Ball in the barrel, and add buckshot to it.
If I were working on a load, I would be test firing at 15 yards, and begin with a 75 grains load of powder, the single ball, and One layer of 3 pellets and see how that shoots, pattern wise. If the shot is on a 12" square target, then add another layer of 3( total 6 pellets) and see how that shoots, and how you like the recoil. Remember that when you decide what Size Buckshot you choose to use, in this experiment, weigh the buckshot to see how much of an increased in total weight you are putting in your gun. As best as I can glean from reading histories, a Buck and Ball load consisted of one bore diameter ball, and 3 pieces of buckshot. The idea was when shooting at the enemy, which were arrayed in front of each other in ranks, standing at shoulder width, you use B&B loads to increase your chance of hitting someone, and if you were lucky, 2 soldiers. Any wound made that soldier a "casualty", because the lack of antiseptics, and anti-biotics meant that many "wounds" would eventually kill the soldier wounded as a result of long term infections.
Unless a wound was a grazing wound, a wounded soldier was considered the same as a dead soldier, and no longer expected to continue in the fight. Of course, not all enemy combatants obeyed, or even understood these " rules of war", and slaughtered any wounded enemy soldier whether he could resist or not, and whether he did resist or not.
For hunting, buck shot in general, and buck and Ball loads in specific, are rarely affective much beyond 10 yards. You are more likely to wound a deer( buck) running past you in heavy cover, than to deliver a mortal wound, if you miss with the single RB. Many of us refuse to take shot at running deer, choosing to wait for a shot at a game animal that is walking or stopped. :hmm: :hatsoff:
