Reply With QuoteApparently you can, just neck size them and then fire form them, there is a difference, It becomes a 7-300 or a 7-270 and is not the same as a true 7mm WSM, Hey as long as if fits in the chamber I will make it conform, LOL
Dean
Hi can I use 300 or 270 WSM brass and size it to 7 WSM or is there more to it.
Tanks Dean
RUMs are like woman in Stiletto heals, you know they are going to put you in the poor house, but that has never stopped anyone from pursuing them.
Apparently you can, just neck size them and then fire form them, there is a difference, It becomes a 7-300 or a 7-270 and is not the same as a true 7mm WSM, Hey as long as if fits in the chamber I will make it conform, LOL
Dean
RUMs are like woman in Stiletto heals, you know they are going to put you in the poor house, but that has never stopped anyone from pursuing them.
i know 270 wsm and 300 wsm brass is the same except for neck dia.
i use 270 brass in my 6.5 wsm with no more effort than a trip thru
a full legnth 6.5 die.
i was of the opinion the 7mm wsm held more powder but i could certainly be wrong.
i do know the norma brass takes more pressure than does the winchester at least in my gun.
Yes straight 7mm holds more powder than the resized.
Dean
RUMs are like woman in Stiletto heals, you know they are going to put you in the poor house, but that has never stopped anyone from pursuing them.
Sorry Dean, I thought someone else would have answered this by now.
The 7mm version has a different shoulder height measurement than the 270 and 300 WSM's. But it can be done using the false shoulder technique. Let me know if you don't know how to do that. Also monitor neck thickness when you do it.
Is brass hard to come by for the 7mmWSM right now?
Yes brass for the 7mm is a little scarce there is some 300 and 270 around, and yes I would like to know more about that false shoulder, if you please,
Tanks Dean
RUMs are like woman in Stiletto heals, you know they are going to put you in the poor house, but that has never stopped anyone from pursuing them.
To create a false shoulder on the 300 wsm brass, size the neck to where the new shoulder position will be. Here's a pic of the 3 steps on a different case. With 270 brass you'd have to neck up first then back down to 7mm to create the false shoulder.
Why do have to create a false shoulder, why can't you just fire form the brass, like an Akley improved shoulder.
Dean
RUMs are like woman in Stiletto heals, you know they are going to put you in the poor house, but that has never stopped anyone from pursuing them.
I'm willing to bet that you can dean. If I remember right its not much different than the 270wsm. Just different enough so people couldn't chamber a 7mm in a 270 and blow themselves up. Kinda like the 280 rem and 270 win same case just slightly different.
That was the main reasoning behind a 300RUM and a 338RUM, just enough that you couldn't chamber it, so it's the same only different.LOL
Spanky
RUMs are like woman in Stiletto heals, you know they are going to put you in the poor house, but that has never stopped anyone from pursuing them.
I don't know what the dimensions are of the 7mm vs 300 wsm are so take this for what it's worth. With other cases I've done like the one pictured, the false shoulder creates a positive stop for the case to headspace off of and a better fill-out of the chamber afterwards.Why do have to create a false shoulder, why can't you just fire form the brass, like an Akley improved shoulder.
With an Ackley chamber it's designed to slightly crush fit the standard case to begin with so it's already set-up for you. When the shoulder needs to get moved forward like in the pic, something has to stop the case's forward movement. A jammed bullet works ok. On that case in particular case the rim can but I've found that the finished headspace is better and more consistent with a false shoulder than the other methods. That's important if the case has straighter sides like an Ackley. If the headspace isn't right after the first firing, they don't grow in length very well because of the extra friction.
A false shoulder isn't needed all the time but when the shoulder needs to be moved forward a fair amount or there isn't anything else to positively headspace off of it's a handy little trick.
Here's the difference between a 300wsm neck sized to 7mmWSM and a regular 7mmWSM. False shoulder gives a better fireform with reduced loads and it also holds the case face against the bolt face for more consistent primer ignition.
It's also a very good way to get great Norma brass in 7mmWSM.
"Muzzle velocity is a depreciating asset, not unlike a new car, but BC, like diamonds, is forever."-German A. Salazar
If you try it without the false shoulder, it could cause case head separation when the case stretches to fill the chamber....or shortly there after...maybe one or two loads later. The old way was to jam the bullet hard into the lands. But the case is still driven forward when the firing pin hits the primer that way. It can still stretch the brass as it expands to take up the free space.
With a false shoulder the firing pin will not drive the case forward hardly any if at all.
The 300WSM run into the die of the 7mmWSM should be ready to load and shoot......the 270WSM brass will need to be necked up to 300WSM then back down to 7mm to create the shoulder.
Also, when necking to 7MM from 300, neck it down just enough to be able to close the bolt.....it should be a tight fit so that the false shoulder is pushed FIRMLY into place. That will give the best results.
Keep an eye on neck thickness and over all case length.........should be fine but I always measure just to be safe.
Hope this helps........there was an article SOMEWHERE on the 6mmBR site.......but I can't find it anymore.
Last edited by Apache; 06-26-2013 at 12:41 AM.
Thanks guys this is definitely one of the more informative threads,
Dean
RUMs are like woman in Stiletto heals, you know they are going to put you in the poor house, but that has never stopped anyone from pursuing them.
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