I have 47 pieces of 357 brass waiting now for 6 years for a similar project.
I have very successfully made full length (same as cartridge overall length-COAL) 45 Colt shot shells from 460 S&W brass. (1) In that project the brass is cut off or trimmed to COAL of 1.51", since I used virgin brass a full length sizing was needed. (2) Next a 44-40 sizing die was used to "Tapper" the top 3 or 4 tenths inch of the brass, this is the Bullet area and is smaller than the case O.D. (3) I primed with a Winchester Large Pistol primer. (4) For a powder charge I chose a light load for a 220 grain lead bullet (5.7grains WW231). (5) You need a over the powder card to prevent the shot mixing with the powder charge! I used a .060 thick cork card-common for BP cartridge loading. (6) I scooped a 1/2 ounce of #7.5 shot with a Lee dipper and (7) place a second card over the shot (this was about 1/10" below case mouth) Some people have tried using a gas check and crimping in place. It has never been successful for me! (that check can tip and release the shot, or worse can get stuck in the throat: VERY DANGERIOUS) (8) I sealed the cases with a tube of Gutter Seam Sealer purchased at Lowe's roofing department. I wiped level with case mouth with a popsicle stick and made sure not to get any on the outside case walls. Let dry/cure for 2-3 weeks. The results: from a 5.5" revolver, I got a dense and even 12" pattern at 10' distance and about 750 feet per second. A friend used one of these shells on a West Virginia, Copper Head snake, the shake was shredded at 8 feet. These are totally reloadable.
I had planned to use the 357 Max brass to make 357 MAG full length shot shells. The two things that stopped me were, (1) to tapper the case mouth, I have yet to find a suitable die, and (2) when all is said and done, you will only have 1/4 ounce or less of shot.
If you have a 357 Max revolver, and want to make full brass length shot shells, (1) figure how much shot you will use, fill empty case with shot leave 1/2" at top empty- weigh the shot(2) pick a 357 mag load for that weight of bullet going 700-800 fps. (3) for wads, there are 36 cal. felt wads (get un-lubed wads) about 1/10" thick. Depending on powder charge, you may need to adjust shot charge.
If any of this works out for you PM me with results, or questions. Ivan