i was hoping that I could use 7mm rm or 338 win mag to resize to 300 win mag. Any help would be appreciated.

Your best deal is just look a little harder and find some once fired 300 Win Mag brass.

7mm Mag and 338 are too short.
You might use 8mm Rem Mag, 300 H&H or .340 WBY.
None are very good choices.

There should be a lot of 300 Win Mag brass out there if you look in the right places or just ask here or in the AR classifieds.

I've got some nickel brass I'd be willing to part with. I'd need to look at numbers and number of fires.

Go back to the originals. Use 375 or 300 H&H brass. Trim, neck, and blow out the shoulder

Barstooler

I've been looking too. It seems like there is some available, but at elevated prices. I bought two 20rd boxes incomplete of Speer DWM(?) cases some loaded, some not some missing, because it was all I found around here. I am scrounging .375H&H to neck down.

If you use longer brass, you might need to turn the necks as well.

I have 60 once fired. 46 are RP, 5 FC and WW super if you are interested.
Dave

Anything long enough will be harder to find and more expensive than getting some real 300 WM.

See "Mike Dettorre' rule #1".

I have been buying Norma brass from Brownells. Seems like they get it in rather often.

Thanks for the replies everyone. I finally found some locally.