Here are some 357AR (MaxRimless) cases made from 5.56 LC-13 brass and thought I'd show the steps. A couple of guys have made the cases from 357Max brass which just involves changing the rimmed case to rimless, but I like using cheap 223 and 556 brass. So here's the steps:
1. trim to 1.640"-1.650" and debur
2. anneal
3. lube inside the case and expand case mouth with skinny expander
4. expand case body with blunt expander
5. resize
6. roll case shoulder wrinkle away (optional)
7. turn necks/ream to .0105" case wall thickness
8. trim to final length 1.595" and tumble
9. load/shoot
This method seems to work very well as I had no split cases out of the 40 or so I formed in this batch. Hunting season is just around the corner and I figure I'll make another 100 or so since my son is also shooting them now. Usually I've had around 5-10 cases split out of 100 when using once? fired range mystery brass. Any flaw in the case mouth of the parent case will result in a split since they are getting expanded up so much. The initial trim and debur really cuts down on losses. This batch of LC-13 cases probably would of been fine without turning/reaming, but I've had others like FC cases that wouldn't chamber without turning so I just turn them all. Really all you're reaming or turning off is where the base of the bullet would be. The two expander stems are made from a bolt (it's quick and easy) and some hardened drill rod. They just fit into a Lee 38-357 powder through die body