I've been reloading all brass (Magtech) shotgun shells for about 6 years in 12, 16, & 20 ga. They feed fine through my Win mod 12s w/o crimping.
Modern plastic wads do not fit well (too loose...the case wall are thinner than plastic hulls), so I use oversize fiber wads (18ga in 20ga, 14 ga in 16 ga, & 10ga in 12 ga) from either Circle Fly or Buffalo Arms. Fiber wads don't seal as well as plastic wads, so one needs more powder. I started by using data from before the introduction of plastic wads (1955 +/-). I use an overshot wad sealed with carpenter's glue...no crimp.
There's a lot of data from this era for Red Dot & Herco powders, but not much for more modern powders.
Later I bought a Pressure Trace Unit from RSI & a chronometer from Midway, so I could develop loads using more modern powders.
You have to enlarge (and perhaps countersink) the primer pockets in order for Magtech hulls to accept 209 primers.
Loading all brass hulls is more time consuming than reloading plastic hulls, but I think it's more fun.