I know there is some small differences between the 270wsm and the 7mmwsm brass. Can you resize the 270wsm to fit the 7mmwsm. I have a bunch of Norma brass in 270wsm but no longer own a 270wsm rifle.

The headspace is not the same. The 270 WSM is shorter by about .038". It would not be worth the bother to me.

It can be done but like Savage said it probably isn't worth it.

If you were to try you'd have to expand the neck to at least 30 caliber, FL size in a 7WSM die creating a false shoulder where the 7WSM's shoulder needs to be, load and fireform in your 7WSM chamber.
This would be a 1 time process but you'd still have an improper headstamp.

Sell the 270WSM brass and buy the right stuff.

Thats what I figured. I resized a 270wsm to a 7wsm and it fed easily. But I knew there was more to it. Its a shame Winchester is the only option for 7wsm brass.

It would for me, since like the OP observed, there's only one source for 7 WSM brass.

Nsaqam, what's the reason for having to expand the neck first to .30 or more and FL size, why not just expand the neck to fit a 7 mm bullet and fireform it as is like they do to fireform AI brass?

Since the shoulder of the 7WSM is farther forward than the one on the .270WSM if you put unformed (except for necking to 7mm) .270 brass in the longer 7WSM chamber there would be no shoulder to hold the casehead against the boltface creating a massive excessive headspace situation.
The idea behind first expanding the .270 neck to .308 or larger and then FL sizing in a 7WSM die would be that doing so would then reduce the .308 neck down to 7MM but only as far down the neck as is required by the 7WSM, the remaining portion of the neck would still be sized for a .308 and thus a small false shoulder would remain on the neck exactly where the normal 7WSM shoulder would be. This small, false shoulder would be the portion of case that would come into contact with the shoulder/neck junction in the 7WSM chamber thereby creating a normal headspace condition where fireforming the rest of the shoulder would be possible.

A real AI chamber has about .004" SHORTER headspace than the parent cartridge has and therefore when the parent case is chambered in an AI chamber the shoulder/neck junction of the parent is jammed against the shoulder/neck junction of the shorter AI chamber thus holding the parent against the boltface and creating a proper headspace condition where fireforming is safely possible.

Alot of words and they may be confusing but if you have any other questions or need some clarification feel free to ask and I'll try to help.

Got it, sorry I was thinking it was the other way around, with the 7 being shorter than the 270, my bad.

nsaqam, what's the proper way to expand the neck from .270 to .308?

Just put a .308 expanding ball (I like the smooth elliptical Hornady expanders) in your 7WSM die (or even better a decapping die) but adjust it really low so you don't have to run the case all the way into the die. Just run the case far enough for the expander to fully enter the neck and then back it out. You now have an expanded neck.
Replace the 7WSM expander in the 7WSM die, adjust properly and size just like normal. You'll end up with a false shoulder on the neck and then load and fireform.

Unless you already have a bunch of .270WSM brass you can save the expanding step by just getting .300WSM brass from your choice of manufacturer and size it in a 7WSM die.
Depending on the neck dimension in your chamber you may or may not have to turn the neck. Most likely you will not have to.
As always work up your load, especially if you use .300WSM brass necked down because you may have a tight neck situation.

Thanks!!!!

The 7MM WSM may not be a very popular caliber and it may die off. I have one and I love it. I know every one here hates to waste brass but I would give the brass to someone who needs it or sell it in the classifieds and get some brass with the correct headstamp if your funds allow it. I know someone will blast me for this but I just hate to have stuff with the incorrect headstamp around, if proper brass is available, since I've seen one rifle blow up using the wrong ammunition. I'm glad it wasn't my hands that were holding it. No serious injury, thank God, but very painful and it wrecked a nice rifle. IMHO BT

BT, that is what I suggested initially as well but a coupla folks said that they would prefer to have a choice of brass manufacturers instead of just Winchester which AFAIK is the only source for 7WSM brass.
This can be done by the method I described.

I too am leary of incorrect headstamps but my 338-06 is all in 30-06 brass because of the cost of proper headstamp 338-06 brass. Pretty hard to fit the 338-06 cartridge into a 30-06 chamber though.
The 7WSM and 270WSM should be alright as well considering the longer headspace dimension of the 7WSM.

I'm more concerned about the really hot loaded versions of cartridges that have a low SAAMI pressure limit.
The 6.5x55, 45-70, and several others are commonly loaded way above SAAMI and used with perfect safety in modern actions. These cartridges put into the older, weaker actions could be catastrophic however.

Well, as far as incorrect headstamps, it seems that if you own one chambering in a WSM it would not be cause for concern, as long as you don't leave your ammo. laying around where someone else can get to it. Especially since a 270 WSM expanded to 7 WSM won't chamber in a .270 WSM.

As for me, it won't matter, I just bought a bunch of WW brass in 7 WSM, I'll probably have to do some culling.

Anybody want to buy 270 WSM brass?

Not an expert on redoing WSM brass but it should be possible to fireform to 7mm w/o creating a .308 false shoulder. Size to .284 and seat the bullet out to the lands with a minimum powder charge. Seems to be accomplishing the same temporary headspace goal with one less step. Wave me off if I'm wrong.

I'm very leary of using a bullet jammed into the lands to establish headspace. It may work but I much prefer a shoulder to headspace off of.