Roll crimp finished carts can be made by hand in low volumes easily enough, data and components available from the likes of, clay & game, Folkestone Engineering etc. Youtube is handy too. I've knocked up a few different loads and it's well worth doing IMO. It works on cost and helps the loader fill the gap in the market for smaller shot, #7 #7.5 #8 etc. There's a lot of info on this site http://www.fourten.org.uk
For dispatch, any half ounce or greater load traveling at 1100fps will do for a sheep or deer at close quarters. Don't shoot a big stag or ram in the crown, shoot it between the eye and ear hole angled slightly towards the ear, or the base of the skull angled up slightly into the bulk of the head. At sub 18" the shot is moving more or less as a single mass so for humane dispatch for small to medium size injured animals it'll work fine.
That said, round my way unless authorised to shoot on the adjacent ground, even a mercy, dispatch with a firearm would land such a good Samaritan in the serious trouble. I just use my extending wrench, one well placed good whack with a follow up does it. Shining a torch in an injured beasts eyes calms it, helps it stay still and provides light to see by, while the coup de grace is delivered.
Normal practice is to call out the keeper or farmer/crofter. But I don't know a single one that would thank you for a 3am call out, so blunt trauma is the best all round answer at night, in remote locations or both.