Does anyone know of a .30 cal cartridge based on the .357 max cases. I belive there is one called the .3o r-c max but can't find anything on it.

There are several out there.
30X357 Max
30 Max
Jim Rock of RPM chambers for some variation of these and used to sell dies.

I have a 30 357 Max long or 30X221R long. It was created on a small Martini action. I like to have never figured out how to make brass and then once I got a set of 30X221 dies I just kept playing until it chambered and fired to the proper length. The last batch of brass (luckily only 10 rounds) had splits the length of the case after the first firing on 8 of the cases. The chamber is tight so it must be the brass. Have not shot it in several years. It has a real long neck so I want to make a cast bullet plinker out of it. Builder was a gunsmith who used a match 308 (shot out barrel from a bolt target gun)and built the Martini to shoot Schutzen matches.

Do you know who makes dies for any of them, or where I can get specs? Or maybe case diamentions?

Sharpsfifty
Jim Rock should still have dies for his creation, drawings also. It had a shor neck on full length 357 Max so I would assume it beat the capacity of the case in my gun by two full grains of powder capacity!