Making 7wsm brass out of 270wsm brass - HELP!

[Hasgun Willtravel]

If there is a quick answer, I need one.

I know there is a difference in the length from the base of the cartridge to the datum line between these cases, and the .270 and 300wsm are the same. The 7wsm is slightly longer. From what I have read, this is to keep a 300wsm from being able to chanber the 7, and the 270wsm from being able to chamber in the 7wsm, because of the datum line of the 7wsm, and the .30cal bullet will not chamber on the .270wsm.

Now, i have been reading about the cream of wheat fire forming method, and it is not creating enough pressure to make the 270 wsm grow to index on the shoulder of the chamber, as new 7wsm brass does. It also smells like burnt hair, which is causing some concern and anxiety from the wife.

Unfortunately I do not have the tool to tell how much it is growing, though I know it is not reaching the shoulder in the chamber yet, by using the "smoke the brass" method taught at hillbilly 101. Judging by the primer, I am reaching some pressure in the chamber where I am not going to go any higher with the powder, because it is protruding, and flat as hell.

Now, my concerns are to load a light to medium load with a bullet into the lands, to create the pressure needed, and to keep the brass against the bolt face, with out having case head separations or gasses leaking back into the action, in return, fucking up my face.

How do I do this safely, or at least as safe as can be done? Fire forming as normal by literally loading up the rounds as usual, but a little lighter, and hope it works out?

I have no experience making brass like this, thanks in advance for the wisdom.

 

[Graham]

I am certainly no expert on this, but couldn't he just seat the bullet to the lands and use a starting full power load that isn't a Max load?

One would think that this would allow him to get some utility out of the fire forming loads as to finding an accuracy node for the powder charge and a seating depth for the bullet without wearing out his barrel doing fire forming of the brass.

 

[long range newbie]

they have different case capacities so you cannot form it from one of the other wsm cartridges I don't remember if its 300-7 or 270-7, search other forms but I did 270wsm- 300 so Idk

 

[Hasgun Willtravel]

the problem is there are conflicting answers on every page I have read on. It is always the same two answers, "yes, there are differences, they are negligible, but I have had great results", to "no, they have different capacities, they are different cases."

The reasons they have different case capacities as I understand it because the datum line to the shoulder is farther up on the 7wsm than the 270 or 300wsm.

I just want to know if I can put 61gr of RE22 into the necked up 270wsm brass, and blow it out to the 7wsm chamber?

 

[Graham]

You can neck-up 270WSM or neck down 300WSM. Both make 7WSM just fine.

 

[Hasgun Willtravel]

And just load a safe load and fire in chamber with bullet to the lands, eh?

 

[turbo54]

Create a false shoulder, and fire midrange 7WSM loads. Bullet need not be jammed.

 

[turbo54]

Create a false shoulder, and fire midrange 7WSM loads. Bullet need not be jammed.

Let me elaborate, now that I've got a keyboard and not a smartphone...

False shoulder: It is crucial you do something to keep the casehead in contact with the boltface when you fire the "short headspace" cartridges, or you'll stretch the case down by the web, drastically reducing caselife and risking CHS's.

So, you can either do this by jamming the bullets balls deep into the lands, or by using a false shoulder. The false shoulder method is better.

Essentially, you'll be necking the 300WSM case down to 7mm for only a portion of the length of the neck. You'll need to adjust the 7WSM die so part of the neck remains 30 caliber. You want the "neck up" to occur such that it will be in contact with the shoulder of the chamber. Thus, the cartridge will be clamped into the chamber between the boltface and false shoulder you've created.

If you start with 270WSM, you'd want to neck it up to 30cal, and then neck down according to my statement above.

Case capacity and charge: The 7WSM absolutely has more capacity than a 270 or 300WSM. However, it is my experience with improved/wildcat cartridges that the smaller case "acts" nearly like the larger one it becomes during fireforming.

Example: Most 6xc loads are ~39 or 39.5gr H4350 with a 105. That amount of H4350 easily fits into a 6xc case, but even 38gr (a typical FFing charge for 22-250 --> 6xc) is compressed in the non fireformed 22-250 case. 38gr would be way overpressure for a 6mm-250 cartridge fired in a 6mm-250 chamber, but yet is NOT overpressure when fired in the much larger 6xc chamber.

Thus, even though the 300WSM cases you're FFing have less case capacity than 7WSM, because the chamber is bigger, the case will blow out to fit the chamber pretty darn early in the firing event, increasing the effective capacity of the case.

Still, I wouldn't run "full tilt" 7WSM loads, but you don't need to back down much. Also, don't forget the percentage difference in case capcity between a 22-250 and a 6xc is WAY WAY bigger than the percentage difference between a 7-300WSM and 7WSM. You'll be fine.

 

[former naval person]

As Turbo says...the man knows his business. I find an easy and more concentric way to expand the necks of the smaller round is to buy a K&M expanding mandrel. About $17 last time I looked. I used that method to form my .375-06 Imp. I also had to expand .35 Whelen Remington cases to .40 and neck back down because my singleshot .35 Whelen chamber was longer than the datum on the factory brass causing numerous misfires until I fit the brass to the chamber.

 

[Hasgun Willtravel]

Thank you Turbo, that is the explanation I have been looking for.