Sizing 300wsm cases to 7wsm

[muffo]

Can some1 tell me the exact process of sizing 300wsm cases down to 7wsm and the dies / tools needed to do the job

 

[Elkbane]

If you already have your 7mm WSM dies set up the way you want them, you can just use your 7mm WSM die to neck down the 300 WSM case. Be aware that the shoulder on the 300 WSM case is 40 thousands shorter than the 7mm WSM case. The 7MM die will create a "false shoulder" on the resized 300 case. If it were me, I'd neck down without using the expander ball in the sizing die, then expand with an Expander mandrel (K&M or Sinclair).

That shoulder will be the new location of the shoulder/neck junction on the fireformed case once it's fired in the chamber. The false shoulder is supposed to keep the case from stretching at the web, but for good measure, I'd load the fireforming loads with the bullet into the lands and use a mid-range load of your normal powder for fireforming. That will keep the base of the case firmly against the bolt face when you fireform.

I have a few 300 WSM Norma cases sized that way, but haven't shot them yet - still hoping the 7mmWSM Winchester cases will work OK, but I'm having my doubts.....too much neck thickness variability for my tastes.
Elkbane

 

[XTR]

Are you trying to use 300WSM cases in a standard 7WSM? I know of a number of folks who have wildcatted a 7/300WSM to use the same shoulder as the 300WSM

If you're doing it in a standard 7WSM that seems like a long way to blow out the shoulder.

 

[Elkbane]

The OP wrote 7WSM, not the 7/300 WSM configuration. Actually, it's 37.8 thousandths. Not near as far as fireforming 30-06 cases to make 280 Remington (51.2 thousandths) or fireforming 280 Rem to make 280AI (shoulder corner moves 97.4 thousands).

But it does sound like a big number.....
Elkbane

 

[muffo]

Its standard 7wsm with a 313 neck. Im still waiting on the barrel arive and be chambered so im ordering dies and some other loading gear but I have never done any case forming so I thought id ask to get a detailed explanation before I order my loading gear

 

[Elkbane]

WIth a 313 neck, I'd use Winchester brass and you'll probably still have to turn the necks. My lightly turned Win cases measure .312 on a loaded round, and I'd like to turn them a little more to get consistent neck wall thickness (can't - doesn't work well with my die/chamber setup). Norma brass is going to be too thick for your chamber.

You want at least 2 thousands clearance across the neck on a loaded round. So, .313 - .002 = .311. Less the diameter of the bullet (.284)/2 = 13.5 neck wall thickness.

I just sized down some lightly turned (just cleanup) 300WSM Norma cases last night and the loaded round was .314" across the neck. That won't fit in your chamber. That equates to 15 thousandths neck wall thickness. You could make that work and have them really uniform, but you'd be turning 1.5 thousands off the neck, which is quite a bit.
Elkbane

If I had a 313 neck (mine's sloppy factory - .320), I'd be using Redding Type S F/L dies with a 310 Titanium bushing......

 

[muffo]

Thats why I did it so i could turn a fair bit off the neck and get it really uniform, Im also hoping I might be able to use some winchester brass but I dought il get the accuracy from it. I can get winchester brass for about 60 cents and norma for 2.90 so Im going to try the winchester first