I have been using brass hulls for more than twenty years. I have used Magtech brass as well as hulls from the old Brass Extrusion Labs Ltd. I have, in addition, a bunch of zinc hulls made by Alcan.
The best hulls by far are those made by Rocky Mt. Cartridge Company. They are also the most expensive at about six dollars each. They are worth the expense. The RMC hulls are lathe turned, true to bore, and use regular 209 shotshell primers, and can use modern shotshell wads and smokeless powders. Given proper care, you will use them for the rest of your life and then leave them to your kids. You can use modern reload data for straight walled hulls.
Using BP, you need 12 Gauge wads and cards, though plastic wads will work. BP is not kind to plastic and it melts and may leave plastic deposits in the bore.
The most commonly available brass hulls nowadays are the Magtech hulls....more readily available and substantially less expensive.
The Magtechs are drawn brass hulls. This means that, though they are 12 gauge hulls, the interior of the hull is larger than 12 gauge. Modern 12 gauge components are too small to work properly. One needs to use 11 gauge components. Thus, one must use/build a traditional wad column from cards and wads (available from Circle Fly Wads or Ballistic Products Inc.). They are primed with large pistol primers. They are designed for use with BP, though I have used light loads of smokeless.
Both the types of hulls, once loaded, are sealed the same way....a thin "overshot" card which is sealed with glue. I use Duco cement. I have tried Elmer's Glue, and Waterglass (liquid sodium silicate). They work. Duco works better.
When I use the Magtech hulls and BP, I load two and three quarter dram loads - about 70 grains of FFg BP. The hull is primed using an antique priming tool. More about that in a moment.
After priming, the powder is measured and dropped into the hull. On top of the powder does an 11 gauge "nitro" or over powder card - stiff cardboard about 0.135" thick. Then there are 11 gauge fiber wads atop that....how many are used are a function of how much shot you load. I use one 1/2" wad and another one split in half so as to make 3/4" total. Then I drop 1 1/8 oz. of shot. Last comes that overshot card. I use a 10 gauge card for a tight fit and seal it round with Duco.
Priming - even without a special tool, priming is still easy. You need a flat hard surface and a metal or plastic tube about six inches long. You put the primer on the hard surface, place the hull over the primer so the primer pocket lines up, put the tube into the hull and, gently, tap the hull onto the primer.
ballistic products inc has a manual about reloading brass hulls.
Note: do not roll crimp these hulls. The crimp will not come out and will make reloading them very difficult. How do I know this?
Pete
Reloading tools for Magtech hulls from EBay;