10mm Magnum (10mm Mag) from Starline 6.8 Basic Rifle Brass

Mod'd my S&W 610 to take 40S&W, 10mm Auto, and now 10mm Magnum, a bit of a wildcat round that is comparable to the Remington 41 Magnum. Although I found some range ammo, I was curious what parent round I could use to make 10mm Mag. The 6.8 SPC is a good candidate, as its parent case, the .30 Remington, is the parent case to a bunch of things. But, the 6.8 is a tapered cartridge, and fireforming would be the go-to solution to expanding that case. Thankfully, Starline Brass sells a basic case that isn't formed, so it's apretty good fit for making 10mm Mag brass. The best thing to do, is buy the brass for what you want. But this pistol/revolver brass is not available anywhere right now. Ergo, why I am playing with this solution.