The 7mm Wby is a full 1/10" longer than the 7mm Rem Mag.
If you use this case and fire form it it may even get shorter, and that is not good for accuracy because the short cases will form a hard carbon ring in the chamber in front of the short case.

The best way and I have done it is to use 300 H&H brass and a shortened 300 H&H die with it you push the shoulder down to the neck radius. Trim the cases 0.015" long, anneal the neck and shoulder 650F.

Then run them into your 7mm Wby die and fire form them with Cream of wheat. Cases a forced into the neck transition because the cases will shorten about 12-15 thou. After fire forming the cases will have to be trimmed again.010" less than chamber lenghth. You may not have too, but I always do a minimal 75% outside neck ream.

If you want to use 7MM Rem Mag brass have the rifle chamberd for this case, that is no big deal either. But the Wby case has a much better neck length. Fred M.

Retard, I once reformed 100 pieces of winchester 300 magnum brass into 7mm weatherby brass by using an rcbs 7mm remington magnum trim die to size the first step. (The remington die version had a similar shoulder to the parent case that seemed to crush less cases than trying to just use the weatherby die to form in only one step.) I then used a 7mm weatherby full length sizing die to form the weatherby shoulder onto the case. This system worked well enough that only a small percentage of cases were lost to crushing.

The cases then needed trimmed to length.

Next it is important to use an inside neck reamer to cut out the too thick neck. The too thick neck is caused by the fact the rear part of the new neck is formed clear down from the full width case body of the parent case, because the 7mm weatherby case is shorter than the parent case. To be able to use the inside neck reamer required the case to be fire formed, so I used 130 grain speer boatails barely seated into the front part of the neck that was thinner to allow the fireforming, then the reaming was properly done.

Those cases lasted 12 plus firings, when they were retired. They still appear fine. All sizing was done with a slight crunch fit to ensure good cartridge headspacing.

By the way, you will notice the 7 mm weatherby is a nice round. Have fun.

Widowmaker.
Instead of fire forming with the thick necks I would expand the necks with a K&M Expandreon and than outside neck ream rather than the inside reaming. Inside neck reaming will not make the neck walls the same thickness all around, hence your loaded ammo will not be concentric with the bore or chamber. This is by the way the accepted accuray methode for forming cases where the necks are made with part of the body. Fred M.