I have used 444 marlin brass, but it can be hard to find, I looked not long ago and couldnt find any, anywhere. Or was way over priced. 303 does make a decent but funky looking 410 shell, since the base never really expands, so has a reverse bottleneck to it. And complicates loading since the wad that fits the narrow section is way undersized for the flared section.
But the best ones so far are ones made from 9.3x74r. They fire form into a beautifully straight walled shell. Fill pretty much the entire chamber, vs the others been quite a bit short. And more room inside than you know what to do with. A full charge of lil gun, a good stack of wads cut from cardboard and plastic, theres still room for more shot than your gonna find load data for. Almost an ounce, depending on your wad stack.
I use a stack of 3 40 cal RB in them, 4 will fit if you wanted them to.