I've been searching for loading data for brass shotgun shells and not having a whole lot of luck!
By way of introduction, I'm a machinist/toolmaker/hobby gunsmith who learned the basics of handloading (and gunsmithing) from a careful and very talented gunsmith/mentor who'd impressed upon me the need for caution and safety around firearms, whether in the field or at the range, also on the workbench, and especially while reloading! I purchased and studied the classic gunsmithing books, rebarreled and rechambered a couple rifles, handfiled and handcut dovetails and extractor grooves, recrowned barrels, learned to fit and bed an action and barrel to a semi-inletted gunstock blank - all under his supervision. Whenever we'd go down in his shop and work, he'd talk common sense about guns, and because even in my teens I'd developed a love for early, vintage cartridges for which (at least back in the '60's) there wasn't always good up-to-date loading data, he'd explain how to safely transpose old loads with no longer available powders & components, to utilize newer components. He'd published articles in Gun Digest and I'm guessing in other publications also, and I stood in awe at his knowledge, and he drilled into me the need for extreme caution when dealing with anything new, untested and unproven! I was young and had a burning desire to move up to Alaska or British Columbia more than attending one of the gunsmithing schools or colleges - didn't make it that far north, but ended up (for what I'd thought would be a couple year stop enroute!) in Maine. Forty years have passed since I first knocked on Chris's door, I've hunted every inch of my old 100 acre farm during the past 30+ - some years too intently and others just barely. I find myself now, with my daughters grown and moved out and with an understanding wife who grew up in a hunting and shooting household (and a young Springer who loves Partridge), as fired up and excited about shooting and guns as I was 40 years ago! I still have a couple of my Marlin levers, my Ruger revolvers, my Rossi 12 Ga. Hammer double, and a batch of those addictive (for some) NEF/H&R break open single shot rifle/shotguns. I now have better than a half dozen factory fitted shotgun barrels in 12, 20 & 410 gauge, also more than a dozen barrels in centerfire rifle & pistol calibers with reloading tools and components to match. All of my cartridges are rimmed, only a few bottlenecked, with most of them straight walled brass…including shotshells. I'm not a Cowboy action shooter and the only blackpowder I load is in my .50 cal. Muzzleloaders. I do enjoy handloading and then shooting from the bench out back, but I'm really just an old wood's loafer who loves wandering around in his fields and woods with a rifle or shotgun in hand, and outside of deer season with my dog too. I tend to get a little too windy when I post on forums - apologies for that, but I wanted to introduce myself and establish my credentials as an older and a little eccentric, but somewhat knowledgeable and probably overly cautious gun nut!
I do realize that this is a shotgun forum, and I am all set and comfortable with my rifle and pistol loads, but being a little eccentric I've been lugging around 30+ REM-UMC #12 BEST once fired brass cases for the last 25 years and had machined a set of handloading tools for 12ga. Brass shells from a nice article in my 1964 Handloader's Digest. About 15 years ago I also bought a new commemorative tin of "Ducks Unlimited" 12 Ga. Brass loaded shells (before they became collectible!). They're specially headstamped REMINGTON DU 37-87, for the 50th anniversary and have no markings on or in the metal tin stating what the load is, but the small paper label on the bottom reads: MADE IN BRAZIL. Obviously we're at the Magtech connection, so I proceeded to the Magtech website once again to search for all brass loaded shells but only found plastics for loaded ammo. I'd previously attempted to contact Magtech USA via the email address they provide but never received any responses, so back to square one. If anyone has experience with these DU shells, either original literature or firing or disassembling one please post same, as I found nothing after a couple web searches. I plan to section, mike and compare 1 each of REM-UMC and the new MAGTECH brass cases, plus one of the DU (after breaking it down to see what they used for wadding and shot charge), also to fire one factory DU load in each in my 12's to measure case expansion as a comparative standard. I've purchased an additional 50 12 ga.Magtech brass unprimed cases and am waiting for 50 ea. backordered 20 ga. and 410s to arrive. I have some shot on hand, and have spoken to Craig at Circle Fly Wads and am ready to order traditional paperboard and fiber wads in appropriate o'size dias. for thinwall brass shells. Dave at Rocky Mountain Cartridge feels (apparently from our conversation) his heavier walled turned brass shotshells are far superior to other brass products, in that their inside dia. duplicates plastic/paper sizing permitting the use of standard dia. modern wads instead of special oversize 11 or 10 ga. as required by the traditional thinwall 12ga. cases. I've long been an admirerer of the English Paradox doubles and was thrilled to see that somebody was working on a grease grooved traditional slug (Dixie Terminator)! for rifled shotgun bores and had planned to have RMC run me 10 or 20 ea. of 12 & 20 ga. Cases, fitted to the chambers of my rifled singles, with an i.d. sized closer to slug/bore dia., and with a heavier base/web and probably with large rifle primer pocket, and with the headstamp: 12 (or 20) BORE PARADOX !! I do agree with Dave in this case, that for a heavy slug load his cases would be far superior to the older thinwall type and wouldn't require excessive resizing, though would require standard dia. wads (which will end up being an undersize non-standard for me!)
Now back to my opening statement/question in this post: "…loading data for brass shotgun shells…" I've spent hours on the web, searching this and other forum archives, also using standard search engines, poured through local libraries and through my 40+ year accumulation of handloading books, guides and magazine articles and found very little info. What I did find generally refers to Alcan or Rem all-brass shells, Alcan or handcut wads, mixed comments on wad pressure, waterglass (sodium silicate) preferably or Duco cement to seal overshot wad, many comments to the effect that "Powder charges recommended for the regular cases are quite satisfactory to be used with an all brass case.", most powder recommendations are for Alcan AL-5 and AL-7, Dupont Bulk Smokeless or Hi-Skor, one or two Red Dot, and always black powder - lots of questions here. I've never been much of a shotshell loader but have noted that much of the published data states to never substitute wads or hulls?
I plan to load all brass 12ga new Magtech 2.4"and once fired Rem 2.5", 20ga.new Magtech 2.4", .410 bore new Magtech 2". Primers are all large pistol and I'm open to suggestions as to maker - years ago, without going to a magnum primer, I guess Rem might've been a little hotter? Regarding powder types and charges, only Red Dot and Hi-Skor are currently available (what was the then new Hi-Skor in 1964 - same as current Hi-Skor 700X, or 800X?) - how about PB, Herco, Unique - for .410 how about 2400 and 4227 (I always have a can of Unique, 2400 and 4227 around!)? Circle Fly wads are available in 11 & 10 gauge for the 12s, 19ga. for the 20s, .410 or larger for the .410s, and include 1/8" Nitro Card, ½" Fiber Cushion, 3/8" Fiber Wad (a little denser than the ½"), and .025" Overshot Card, and I plan to build wad column height tall enough so that overshot will fall just below end of case, to facilitate a bead of waterglass or Duco or ? to seal and secure same. Wad pressure in these brass cases from what I've found seems to be more a function of secure seating against powder charge, interference fit of o'size wads, and sealing medium on overshot wad. I don't own any pumps or autos and as my shotguns are all break open I don't intend to crimp or roll the mouth of any cases. I don't (but probably should!) shoot Trap or Skeet, no waterfowl/migratory, mostly partridge, maybe a bunny once in a great while, probably eventually Turkey and possibly some buck for larger varmints(will deal with those loads when the time comes). I'm only planning to use lead shot and don't see any need for a plastic shot container/bore protector (with one exception - .my 45/410 rifled barrel, planning to use .444 Marlin cases blown out to .452 at the mouth -.452 dia. lead slugs at warm pistol velocities without reverse rotation rifled choke, with choke .45 cal. Speer Empty shot capsules or a wrap of Mylar film?). I'm planning on mild loads primarily and generally shells will be fired in the same gun, so I don't anticipate any need for case resizing.
Those were my parameters and knowledge or assumptions, and the loads I'm looking for follow below:

12 Ga. - 1-5/8 to1-3/4 oz. heavier shot/buckshot moderate vel.
- 1-1/4 to1-1/2 oz game load " "
- 1-1/8 oz " " low/mod. "
- 1 oz light field load low "

20 Ga. - 1 oz field load mod/high "
- 7/8 oz light field/skeet low/mod "

.410 bore - 3/4 oz field load mod/high "
- 1/2 oz light field/skeet low/mod "

I'd like to come up with some brass case slug loads also: 12 ga. w/ traditional Lyman hollow base in smooth & rifled bores, and will wait for 12 ga.Dixie Terminator to be used in special RMC turned brass case and fired out of NEF single Tracker II (rifled bore light shotgun barrel on SB-1 low pressure shotgun frame), and finally one of those grease grooved "Dixie" slugs but in 20 ga. this time and again out of a RMC turned case, but fired in NEF's rifled bull barrel mounted on a late model/high serial # blued SB-2 frame (same action as used for .444 & .450 Marlin, and some other high pressure large base dia. rounds)!!
I look forward to any info on some shotshell loads - if I'm ever going to load and test and pattern before Fall, figure I better start now

Thanks, Joe