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The Handloaders Bench > The First Stop > Technical questions about the site > converting brass: 7mm Rem mag to 264 Win mag

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converting brass: 7mm Rem mag to 264 Win mag
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 Posted: Tue Sep 8th, 2015 10:02 PM
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ingalls.ok2014
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Have a Win model 70 264 and have bought a sizeable number of 7mm Rem mag brass. Is it possible to convert 7mm to 264 safely? Have looked through my sizeable library of reloading books without finding any articles on this subject.:confused:



 Posted: Tue Sep 8th, 2015 11:30 PM
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Rockydog



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Yes you can convert 7mm mag to .264 just by running it through the .264 sizing die. However, You may have to turn necks to allow them room to open in your chamber. All of that 7mm brass in the neck has to go somewhere when you size it down.

Measure the neck of a fired, unsized, .264 case from your rifle and then measure the neck of a loaded .264 round made from 7mm resized brass. If the loaded 7mm reformed brass is the same size or larger than your fired case it most likely needs to be neck turned. The neck must open enough to release the bullet. If the chamber is so tight that it can't open enough to release the bullet pressures can go through the roof and might even damage your gun or you. RD



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 Posted: Wed Sep 9th, 2015 01:34 AM
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ingalls.ok2014
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RD. thanks very much for your reply. Had looked at dimensions of each casing and saw how close they were to each other. Have loaded for many years and have done some case forming, mainly 8 x57 mauser made from 30-06. Considering pressures for 264, I wanted a second opinion on converting 7 magnum. The 7mm brass is from various manufacturers purchased from individuals and will surely have different thicknesses in necks, requiring measuring and turning for consistency and safety. Your thoughts are appreciated. ingalls



 Posted: Wed Sep 9th, 2015 01:58 AM
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Rockydog



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ingalls, You make a very valid point about the different brands of brass having different thicknesses.

I routinely turn .270 and 30-06 brass into 6.5 Gibbs brass but most Gibbs reamers are ground generous enough to avoid neck turning even from the 30-06 brass. The downside? I lose a fair amount of brass to split necks. Annealing definitely helps.

I suspect you'll get by with at least some brands without neck turning. RD



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 Posted: Wed Sep 9th, 2015 01:59 AM
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Donnelly's Handbook of Cartridge Conversions says to form from .300 H&H Mag, just run through the sizer die and trim to length. Funny, to form 7mm Mag from the same case, he suggests (strongly!) to check neck thickness after necking down. I don't think there will be much of an issue just necking down from .284 to .264, but I'd check the neck walls anyway, err on the side of caution.



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 Posted: Wed Sep 9th, 2015 03:29 AM
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Rockydog



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Charley, Donnelly's book is about the best out there, and a great resource, but there are more than a few omissions and errors in it. Your finding there, on this topic, is likely one of them. RD



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 Posted: Wed Sep 9th, 2015 03:30 AM
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I reform WW 7mm rem mag cases to 257WBY cases, without turning, I gain less than .001" in neck wall thickness. I do however have to ream donut from inside neck, when going from 308 to 243.

I've had much better luck, using new brass, but annealed brass should also work.

You will work your brass slightly more, using normal FL die. If you used 7mag die to size body and adjust 264mag die to just neck size, you would avoid much of this.



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 Posted: Wed Sep 9th, 2015 12:59 PM
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Charley



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I use it only as a very basic guide, and double check everything with a second source. Nonte's guide is/was a lot better, but was limited to cases he actually converted, mostly handgun, it seems. Haven't seen a copy in a long time, wish I had one.

For a wide range of opinions on conversions, I'd recommend heading over to castbolits, and checking out the brass forming/reforming forum. Some great (and some not so great) suggestions on getting from A to X.



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