I know that you can make 7.7 brass from .30-06 because I have done it.
I also know that it is not 100% safe, UNLESS you are shooting fairly mild loads because I had 2 cases to rupture, maybe split or crack would be a better description, right above the head on the first firing and several others looked really bad. Was it a bad gun or bad chamber? I don't know, and at the time I didn't care. I quit while I was ahead and bought some Norma 7.7 brass. No more problems. The gun that I had was not safe with the .30-06 cases. Just for info purposes, the cases that failed were all once fired Winchester.
The above being said, if I were planning on shooting nothing but light cast loads, I would use military brass. Maybe I am wrong, and if so I appologize in advance, but they seem to be the toughest stuff around.
Steve