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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/02/2012 at 17:26
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If you have a very tight neck custom Rifle, can you use 7 mm brass and neck it down to a 257 ?? 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/02/2012 at 18:26
Alan Robertson View Drop Down
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.7mm what->> to .257 what? 7mm Roy? Firebird to Scramjet??

Necking down won't gain anything and will likely make your neck thicker...
so will weight training.
If you have a custom with tight neck- you will likely have to turn down and maybe even ream your necks. Can you talk to the guy that built the rifle?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/02/2012 at 18:58
Alan Robertson View Drop Down
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Were you asking about maybe forming .257 Roberts from 7x57? There are several possibilities of 7mm>.257 and more info would help.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/02/2012 at 20:39
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Necking down won't gain anything and will likely make your neck thicker...
so will weight training.
If you have a custom with tight neck- you will likely have to turn down and maybe even ream your necks. Can you talk to the guy that built the rifle?>>>> thanks i do not want to start Destroying  fed. weatherby brass.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/26/2012 at 03:17
Stevey Ducks View Drop Down
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Sure can, but you will probably need to turn the necks down which is not a real big deal. There are several tools out there that will work. Look up the neck outside diameter from your reloading manual. When the necks are turned correctly a bullet will just slip fit inside a fired case -- stop at that point. Excessively thick neck walls can jump pressures up so be careful. Excessive turning will reduce neck tension enough so the bullets will fall out of the case or can be pulled out using no tools.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/27/2012 at 18:44
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The 7x57 is the parent case for the .257 Roberts so sizing down will still work as well as ever.   Necking down will make your new necks about 10% thicker than the original.  Most factory necks run about 13 thou so your new necks will likely be around 14.3 thou, not a lot of difference and if it matters will depend entirely on just how tight your custom chamber is.  I would really dobut it's any tighter than SAMMI specs and you will be fine.    But, reform a case or three and make dummy rounds of them.  Mic the necks and record the diameter.   Then mic a fired case and compare the diameters; if your new necks are at least 2-3 thou SMALLER than your fired necks, you'll be good to go.  If not, you MUST turn the necks until they are smaller than fired necks.

I prefer to use reformed cases simply because they ARE thicker than normal, that permits an improved chamber fit.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/08/2012 at 12:57
Clark View Drop Down
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I  have sized Remington 8x57mm down to 7x57mm and necked it down again to 257 Roberts.

It always works in a standard 257 Roberts with .292" chamber neck.


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