I have some of those steel cased dummy rounds in .30/06, as you point out the flash holes aren't drilled, I'd have never thought of those.
There are steel 7.62MM (308) cases also, and they would work too although you can't find them too often. I recently picked up about 20 of them, dated 1956, for pennies. They are usually found as loaded ammo and so you have to consider the UPS to ship them, and guys like to shoot them for some reason so they may cost more.
They may offer some advantages in slam loaders, can't see much use for them with Bolt actions and from what I've heard the laquer coating can soften when fired and if not extracted immediately the cases can get stuck.
O'Connor made his from stainless and if that's what you want you'll have to make them from scratch. The same for belted magnums. I don't know of any steel belted cases.
Steelheads are fun to play with but in the end you learn that there is not much they can do that a brass case cannot do. Sure, you can load them hotter but exactly how much chamber pressure are you willing to put your pretty face up against?
You can't do much about the primer and if it leaks or fails at lower pressure, what have you gained?
And then there is the work involved in making them. Cutting the threads is delicate work and everything has to line up perfectly. After you go through the labor of making one you almost don't want to shoot it.
My interest is mostly academic, but I'm always looking out for ideas on making ammunition components that don't involve the complex machinery used in drawing cases on a production line basis.
The two piece cases made from different materials are fairly common. They are used for dummies, practice, short-range, mob control, and stuff like that. There are also the two piece brass/polymer cases loaded to full power. Someday we may see all small arms cases made from plastic. They make automobiles, boats, and even jets out of plastic - why not cases?
Ray
Shotshells made from plastic with a brass base and rim have been around for decades, even all plastic hulls have been tried at one time or another.
Not sure how the trianglar cross section tround was made, the plastic case in that cartridge performing most of the functions of a chamber as well, it being carried in a V shaped cut in the cylinder and enclosed at the top by the top strap when in firing position.
At least one Civil War era carbine used a hardened rubber (gutta percha) cartridge case , with flash hole for external primer.
Composite cases using a metal base with coiled brass, copper foil, or paper case bodies were around from the Civil War era on to the late 19th century.