ok, i know the 308 is the basis for 7mm-08, i have 300 rounds of brass for a 308 so is there a problem with just running it through a die and fire forming?
thanks

No. I shot my first 7mm08 using necked down 308 brass for around 15yrs and then I found some 7mm08 brass at a giveaway price so I bought it.
It's a little bit short but that's not a bad thing.

It may depend on your 7mm-08. I had two rifles, both Remingtons in the chambering. The one would swallow anything. The newer rifle, a MR had a tight chamber which required cases previously fired to be small-base sized. This was especially true of military brass, something I've used a lot in my 7mm-08s. But as long as the basic brass is a good fit otherwise, simply running 308 through a 7mm-08 die works just fine. (Make sure you lube the necks well with a good lube.)

The purists will tell you that the reformed cases will have thicker walls in the neck whenever you "neck down". This might produce an issue in a custom chamber with a tight neck used for BR work. Then, you might have to turn the necks on your brass to bring them to spec.

But for hunting loads in factory chambers, using .308 brass works fine IME. I've even "necked up" .243 brass to .284 diameter without incident as long as you use fairly fresh brass and lube the necks really well.

Why not just sell the .308 brass and buy some 7mm-08 brass?

I use R-P and LC brass in mine without problem. FC brass has thicker necks and won't work unless I turn the necks.

Remington & Winchester brass worked fine for me...of course at the time I was shooting an A Bolt!

I've reformed 308 Win. brass into 260 Remington. Works well; just be mindful of thickening necks.

Used to do that a lot about 10 years ago when I had an abundant supply of 308 brass laying around. IIRC there were some LC military cases that needed a wee bit of neck turning for the chamber in my T/C Encore. That was just to be on the safe side because they would still fit but the neck O.D. of a loaded round would be just a little more than that of a loaded round in 7mm-08 brass. I thought things may be a little too tight in the neck area; which could lead to some pressure related issues.