I want to get a die made up from the same reamer that will be used to chamber a .300 win mag barrel.

Can I send the smith 7mm rem mag die and have that reamed out then add a .30 cal button or do I need to buy a specific blank die?

Ask your smith. Some dies are hardened, some aren't.

Generally the sizing die needs to be several thou smaller than the chamber to allow for brass spring back. Plus the neck needs to be smaller to create neck tension to grip the bullet.

Every FL sizing die that I have ever used, and that is about 100, has been heat treated hard enough to ruin a reamer.

Back when I was in gunsmith school the reamer makers would make a standard set of reamers for a caliber include a sizing reamer. We made our dies out of cold rolled steel and case hardened them. I don't think a finish reamer would work for dies.

quote:

Originally posted by ireload2:
Every FL sizing die that I have ever used, and that is about 100, has been heat treated hard enough to ruin a reamer.

You probably use truly good quality dies.

(I have re-cut numerous commercially-sold FL sizing dies, of quite a few makes, for various reasons and most of them I have tried cut like butter.)

To make a sizing die, the reamer needs to be reduced by about 0.003, as the others here have mentioned.

About the only thing I can suggest would be to use the reamer on a piece of steel to make a "go" chamber guage to test ammo with, to be sure it will chamber in your gun.

Otherwise, I do not see an advantage of re-working a 7mm die over just purchasing a 300WM die.

www.NewlonPrecision.com

The SS, will require hardening to Rc42 after it's finished, while the 12L requires case hardening.

If you barrel is CM, and you use a SS die, you may be .002 undersize after reaming (chroming not really needed). Have the ID Hard Chromed to a thickness of .001-.002 IF needed (SS only).

With the 12L, your better off having a die (undersize) reamer cut, as it can't be chromed

A roughing chamber reamer will work for the dies.