The 8x60 can be quite a source of frustration as it comes time to load for it.
It seems like all of the guns you speak of are nitro proved rifles though, so we'll just skip the blackpowder 8mm crap...

I have two here, one is a high grade Belgian BLE ca 1939 simply marked 8x60 and B.Blindee - marking it as set up for jacketed bullets.
The other is a Mauser sporting rifle with express sights and claw mounts on a half octagon/half round tapered barrel, reenforcement plates on the stock, double set triggers, horn triggerguard, greener safety...
It's marked 8x60 Magnum, it's noted to have been set up for the steel jacketed bullets. The proof marks say it was set up in the twenties.

BOTH of these rifles are set up for the .318 bullet. I use 30-06 brass in the Mauser and 7x64R brass for the double rifle, they both need trimming and reformation in an 8x60 die, I'm using a set of C&H dies which I've been happy with.

There really isn't much credible information out there on loading for the 8x60 - and there's a lot of jibberish speculation on the distinction between the magnum and the magnum bomb.
I have the sense the only distinction there is what the marketing scheme of the retailer might have been.

I'm still playing with loads for the double rifle. I'm using the 196gr Woodleigh SNRN bullet and things seem like they'll work out with that bullet. I haven't really worked on many loads yet for the Mauser and plan to work up a load for it that'll hit to the express sight at a hundred yards and call it a day.

I'll let you know when that happens, until then my advise is to take 8x57 loads and increase the charge till you get performance that looks right using the express sights. On the German guns, look at the bullet weight stamped on the side of the barrel at the chamber and work in that weight range.

I haven't been out to shoot lately, I'm buried with work and the ultra-overload of cuteness from my eleven month old daughter. Might get out this week to run another load or two through the SxS.

--Tinker