Thanks, DB. Fills in a major gap in my understanding.
Local rabbits here are quite good (pass the plum sauce, if you please) but I've not made
any effort for decades to go after them as I once did, 12ga x #4 shot. Really nothing to them but the hind quarters.
Way too big shot unless you're after jack-rabbits (hares in the UK) Nothing ever bigger than #6. Preferably 7 & 1/2 shot.