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Can I converted 8 X 57 Mauser into 7 X 57 Mauser , the case head and lenght is the same .I assume that I only need to neck down the 8 mm Mauser to 7 mm. The only concern is resize the bullet from .323 to .284 diameter , Is this too much reduction that will cause the lead to seperate from the jacket or causing the bullet to deform ? I resized 8 mm bullet to 7.7 and load them to shoot in Type 99 Arisaka and it seem to work well .
 

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Why would you want to resize a bullet that drastically? Why not just buy bullets in the widely-available 7mm/.284" variety?

It's pretty commonly accepted that reducing bullet size a significant amount will lead to core/jacket separation. I'd strongly advise against 8mm -> 7mm conversion. Even .323" to .311" is a bit too much, IMHO.
 

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Isn't the shoulder on the 7x57 a bit different than the 8x57? And does that matter? I think that you'd be better off buying new 7mm projectiles and selling the 8mm projectiles to finance it.
 

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7,9mm to 7mm cases etc.

The relative position of the 7mm case shoulder is slightly furether back tahn the 7,9mm case shoulder...so full length sizing is the best way to go, and you can even adjust "headspace" especially for some rifles of the pre-1920s era, which have slightly different chamber specs from the more modern ones.

I always size cases "to fit" the chamber, rather than just "Size down to shellholder" method.

This also prevents early case failure as well (over re-sizing and case stretching)

The other thing to remember is to Anneal the cases after sizing (neck and shoulder). The reduction from .323 to 284 creates a lot of internal metal streewsses, which if untreated, will result in "age cracking" sooner rather than later (ie, split necks and shoulders.)

Projectiles...buy them, they are cheap enough. A bullet reduction set-up from Corbin or other maker could cost you between $500 and $1000 for the dies, and a small hand press, and well near $4-5,000 for a Hydraulic press. And the jackets would be loose, and probably deformed as well.
It would be cheaper (relatively) and more effective, to buy jackets, core lead and swage your own... or buy them.

Regards, Doc AV
AV Ballistics.
 

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I agree with Doc av it can be done though with the corbin dies but youd have to reduce them to below 7mm and then rebump them up in the form die which will reform the core tight with the jacket, but its way cheaper just to go buy some new bullets to use. Core wont seperate on firing unless the bullets are softnose thats caused by the bullet jacket sticking in barrel and core flying out, I assume your using fmj military bullets. aaron10
 

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Discussion Starter #8
Thank everyone for the input. If the jacket will seperate from the core and or jacket deformed then I don't think I would like to invest time and money to do that ( although I admit it seem like a fun project resizing all the bullet ) . The bullet in question is 154 grain FMJ pulled from Turkish surplus that my friend give me . I plan to use Lee bullet sizing die which will cost me about $60 for 4 different size. I guess I better use that $60 for factory brass and bullet ,it sure better that pile of deformed bullet .:)
 

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It's not FMJ, but here is an inexpensive choice for 7mm bullets for your 7x57 Mauser.
 
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