I have just received a rem 6mm I also have a 6mm ai that has a tight neck , I have quite a few pieces of brass that has the neck turned but has not been fire formed ! Can I use this neck turned brass in a standard 6mm chamber??? Thanks for any help

Offhand, I can't think of any reason why you can't.

Try it and see.

Odd place to put the particular question.

Knowing much less than Mr. Howell I too can't think of any reason why not.

I do hasten to add that thinner necks may require bushing dies or other special effort to get neck tension right for handloading. That is extra clearance in the chamber may be matched by extra clearance in the die and so less squeeze than desired.

Thanks that's what I was thinking on the bushing because my 6mmai dies are bushing dies , I did find 2 boxes 1 time fired from a friend, spry if this is in the wrong place!!

One of my friends in Sweden overdid the turning of the necks when he was forming some .416 Howell cases from .404 Jeffery brass. His sizing die then wouldn't size the necks down tight enough to hold a bullet.

So now I have 'em, to be necked-down to .375 Howell.

Like Ken said.
You will know it's too much when they split after less loadings.

Brass can be made to fit a particular rifle, alone. But too thin and you may only get a couple re-loads out of it.