I reload 8m Mauser and converting 30-06 brass can be done. I don't know HOW, but a buddy of mine did it and gave me a bunch
This is one of the more simple conversions. You just trim 06 brass to approximate 8mm Mauser length, then run it through the 8mm FL sizer die.
then check again for length. Odds are they'll be just a touch short, which is no problem. Just make sure they aren't too long, and trim them if they are.
I converted a bunch of LC and TW 50s 06 brass to 8mm Mauser a couple decades ago. They worked fine. Work up your loads per normal practice, of course.
Gets a bit tedious using a hand cranked trimmer though. IF I had to do it again today, I'd start with a tubing cutter, and cut off 1/4" that way, then look at trimming, if needed.
Alternate method, if you're flush with cash, get a trim die for 8mm Mauser, then you can cut off the extra 06 length with a hacksaw and finish with a file.
Not a regular standard item, so expect a custom die price if you go that route. Cheaper to just buy boxer primed 8mm brass, or ammo. AFTER i had convered a couple hundred, I found a dozen boxes of RP 8mm ammo for a good price, so I picked that up too. Not as hot as the European stuff, but excellent brass back in the 90s..