I completely disagree with your comment regarding BBs for coyotes. When we could still use them for coyotes in B.C., we shot many coyotes with lead BBs and I don't recall any that were inside of 50 yards that got away after taking a load of BBs. Your pattern will be much denser with 50 to 60 BBs than with 12 to 20 Buckshot.
Okay i copied some of this and pasted from a previous post to save typing it all again but i think it still applies here......
I did try a shotgun and lead BB with a extra full choke here one year.(We can still use them here for coyote but not waterfowl)
Patterned well but i was less then impressed with the performance on actual coyotes.
With The smaller ones and shooting them in the head it seemed to work well enough on them (at close ranges) but with the larger one's even at ranges of less then 30 yards on more then one occasion i had to shoot them more then once and i even lost a couple.
Twice,the same thing happened to me, i called in double's , shot the first one's in the head standing straight on looking at me flattened them and when i swung to shoot the other one saw the first getting back up out of the corner of my eye and had to shoot them again so i lost out on the double's.(had the same thing happen while trying the 22 Mag on them as well)
Never had that trouble with centerfire a rifle before.
To me it seemed like that smaller shot got all balled up in the fur and didn't penetrate very well.
So if it's all you have and you do use it i would try to only shoot them in the head.
I decided along time ago that i much preffered using one of my .22 centerfires and a variable scope with it set on the lowest power setting for the stands that will have close action.
I personnely would even prefer a .22 Mag shooting the 50 grain Federals or 40 grain Winchester JHP's over a shotgun and BB any day of the week and that is definately still not my ideal dedicated coyote killing cartridge. Still better then a shotgun loaded wit BB as far as i am concerned but that is just my opinion.
Not sure of the size of the coyote's where you hunt.Maybe they are mostly small. They are not here. Like i said on the smaller one's here it did work(most of the time). On the bigger one's not so well.
I would rather have less larger shot in the air as long as it patterned well then a denser pattern of lighter more numerous shot.
To me, just because you have a denser pattern of lighter shot does not equate it to being a superior killer to larger shot carrying more momentum and energy at longer ranges.
If memory serves me correctly the last 2 3/4 inch 12 gauge number 4 buckshot shell i cut open had 27 Pellets and the 3 inch had 41 pellets i believe.
So i am not even sure where you are getting the 12 to 20 buckshot thing from.
I guess we will just have to agree to disagree on the topic my friend.