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Fireform .375 RUM brass for .338 Edge?

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Old 07-16-2008, 01:01 AM
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Join Date: Aug 2006
Location: WA
Posts: 42
Fireform .375 RUM brass for .338 Edge?

I just picked up some .375 RUM brass to size and use in my .338-300 (Edge). Before and after I size the brass in my press, the shoulder is around .020 to .024 shorter than my fired brass. I used a Hornady/Stoney Point cartridge headspace bushing gauge to measure.

This is the first time I have checked the headspace of a sized and unfired brass. The reason I am being careful now is I recently switched from Nosler 300 Ultra brass to the Rem 300 brass. On the 3rd firing of the remington I had a cartridge base seperate, and others getting thin in the same spot(about 1/2" up from base).

My first thought was that I had undersized the brass(since I am using a .338 ultra die, it is possible if I wasn't paying attention) I bought the gauge tonight to check the size of the rest of the unfired brass from the group where I had the brass seperate. They were either the same size or less than the fired brass by .003"

Now I am wondering if the 300 ultra remington brass was similarly short for the chamber on initial forming as I am now seeing with the 375 brass. It would explain the case seperation, which should only happen with excessive headspace.

Another note, the fired brass is .001 shorter than the Go Gauge I used to set the headspace on the rifle(Savage 110, PacNor prefit barrel) I also checked headspace on the rifle and it is fine. As well as the fired Nosler brass is the same dimensions as the fired Remington, so headspace hasn't changed.

Long story short. It looks like I'm going to be fireforming for my 338 edge. Does anyone else have this problem? Or any ideas what I could be missing?

thanks in advance guys.
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Old 07-16-2008, 03:47 AM
Silver Member
Join Date: Feb 2008
Location: Oregon
Posts: 168
Recently formed several .338 edge brass from .375 RUM brass. I also have a Pac-Nor 30" straight tube on a savage 110. I would first run new brass through a .375 RUM die to straiten up any dents in bass. Than I would neck it down alittle at a time using a .338 RUM die. I would use my chamber as a guide. Starting out with brass that would not allow me to close the bolt because I had not set the shoulder back enough. Then continuing to adjust the die till it sized the new brass just enough to close the bolt. Once I found this setting I tighten the set screw on the die. It should now be set for your individual chamber. It would seem that since we are necking down brass, any problems with new brass have to short of a shoulder would be solved by the false shoulder we create. I certainly don't claim to be an expert, there are many here that are. This is just what worked for me. Hope it helps. Good to see fellow shooters out here in the Pacific Northwest.
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Old 07-16-2008, 08:31 AM
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Join Date: Jan 2004
Location: Blackfoot, Idaho
Posts: 8,090
6.5 describes it well.

Some, me for one, when using a die for the particular cartridge slip a small shim (~0.1") under the die nut. The nut is set for proper FL sizing. Thus a small over ring is remains ahead of the shoulder to ensure the case is firmly supported at both ends when fire forming.

For me is was a bear to get the die set up for a proper FL resize and not push the shoulder back a schosie bit too far.

Once set up, all that is needed is to insert the shim for the new brass.
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Old 07-16-2008, 09:19 AM
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Join Date: Aug 2006
Location: WA
Posts: 42
Thanks for the replies guys.

6.5, the method you describe would be settig the headspace on the neck side of the shoulder, while I was thinkng of it in terms of the body side of the shoulder. I will give this a try tonight after work. Seems like a good plan to keep from needing to fireform. I'll still have to fireform the ones I have already sized.

Roy, that's a good tip for fire forming. I'm hoping to use a similar method with full power loads now that I am thinking of the headspace more correctly.
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Old 07-16-2008, 05:30 PM
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Join Date: Feb 2004
Location: Pennsyltucky
Posts: 2,625
Roy, a .1" shim seems awful thick to me, do you mean .01?

the main thing i see that you need to do is check the diameter of your neck on a loaded round. they just might, make that probably will be too thick or tight in your chamber. you're going from 375 down to 338 so the neck walls will be getting thicker. something you should check before touching one off.
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Old 07-16-2008, 06:12 PM
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Join Date: Aug 2006
Location: WA
Posts: 42
Dave, thanks for the feedback. I do plan to turn the necks on the 375 before I fire them. I failed to mention that before.

Right now I'm most concerned with the apparent excess headspace problem I had seen with some of my 300 brass, and making sure I did not repeat the same error with this new set of brass.
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Old 07-16-2008, 08:25 PM
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Join Date: Aug 2006
Location: WA
Posts: 42
Update. I just finished sizing to the minimum headspace on the neck side of the brass and I am confident that they are accurately headspaced. Problem solved(hopefully)

The shoulder is a fairly funny shape compared to the shape of the fired brasss and chamber. Will full power loads still be fine for the initial loading of this brass?
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