If you are just starting to reload for shotgun, as has been mentioned - is not like centre-fire rifle - is NO "working up" loads - most all books say to find a pressure tested recipe and follow it exactly - there looks like thousands of pressure tested loads published - and, no substitutions of any component. I notice some loadings information show 5000 psi difference by changing brand of primer. Appears to be about no correlation between pressure and velocity, if you swap components. I have only loaded a few hundred rounds for my 28 gauges - so take my suggestions with "grain of salt" - there are others who claim to know and understand which components can be swapped, but I do not know that, so I do not generally do that - I find a pressure tested recipe and I follow that exactly - brand for brand, size for size. About only exceptions that I can think of, is that I have wads from BPI that are sold as direct replacement for a particular Winchester wad that is no longer made (or at least not easy to get here in Manitoba) - but that W-W wad is called for in various recipes. I was also led to believe that 28 gauge Challenger hulls are actually Cheddite hulls - so I use them interchangeably - rightly or wrongly.
For reloading shot shells, you will normally need a hull, a primer, a powder, a wad and shot. A very few recipes call for an over-shot or over-powder cards (nitro cards), but I do not think those are "usual". Recipes will tell you what brand and size hull, what brand and size primer, what brand and size of wad, what brand and amount of powder. Perhaps oddly, shot size does not matter - apparently, you could load No. 2 Lead shot or No. 9 Lead shot into any particular Lead shot recipe - is the shot load weight that appears to count - not the shot size. I think loading for some buckshot sizes requires placing individual pellets into the load - I think some slugs require over-shot cards and roll crimps - I have loaded neither, so I might have that wrong.
The shot shell reloading process appears to involve pressing out the fired primer which also somewhat "re-sizes" the case. Then a new fresh primer is installed. Then a powder load. Then a wad / shot cup. Then a load of shot. Then to start the crimp - then to finish the crimp. If you did it all correctly - your press all set up with no errors, you get a sealed shot shell that the pellets do not dribble out the crimp, and that chambers into your shotgun. I understand that twisted crimps, leaking shot, bulged cases, etc. are all signs that you used the wrong components, or do not have the press set up correctly. Strikes me as requiring some attention to detail to get set up and to stock up supplies for a particular recipe - then pretty mindless repetition to load hundreds - occasional quality checks, I suppose, to ensure something has not moved or got loose. I am told that shot shell hulls typically give out and can no longer be used when the "petals" for the crimp break off - nothing I read mentions primer pockets loosening, unlike centre-fire rifle.
I have an MEC machine for 28 gauge and Lee machines for 20 gauge and 12 gauge. I notice all of them use a volume system - for both powder and shot - so nothing is weighed - unless you are fussy like me, and actually weigh out what the various inserts dispense - to confirm. My MEC machine has a "Universal Charge Bar", so I had to set it for the volume/weight of powder and the volume/weight of shot that I wanted - and have never changed that for many years - so that "adjustable" feature might be wasted on me - but it might become "handy" if I have to change out the powder that I have been using, or perhaps a different shot weight and recipe. The Lee machines seem to have replaceable plastic (nylon?) rings that alter the volume / weight of powder and shot that they dispense.
