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In for a penny, in for a pound. Spent the $70 for Hornady die set. I see Neck Size dies by Hornady and Redding also available.

I am not seeing why one cannot neck size for this caliber. The die makers seem to make dies for this purpose so what is the problem that these boards seem to think is going on with neck sizing for a 7.5 K31 ?

If the issue is trying to neck size by turning a FL sizing die out a little , then I too have had some problems with doing that for 7.5 French cases and gave up on it. Costs as much to make a screwed up round as a properly resized round.

Thank you.
 

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It has to do with the mechanical force of a straight pull versus that of a standard (rotating) bolt action, I believe. More mechanical advantage on a standard mauser style action over a straight pull. Or maybe not, but that's my current thinking on why not neck sizing for a K31 straight-pull action (someone will be along to correct me soon, if I am wrong or only partially stating the issue(s), I am sure).
 

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I'm also waiting for a definitive answer on this one, Skip.

I have four K-31s, and segregate the brass for each one. I FL size on all the brass, but am really wondering 'why not?' when it comes to neck sizing on brass that is specific to one rifle alone. I can defintiely see FL sizing once the shoulders need bumping back, but I really wonder about all the other times in between.
Pat
 

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Neck sizing considerations in straight-pull actions.

Lacking the large, direct-attached crank handle of the usual turnbolt action, straight-pulls are somewhat intolerant of tight-fitting cartridges. When a cartridge is fired, it expands to fit the chamber. The higher the chamber pressure and/or the softer the brass case, the closer the fired case conforms to the chamber. In addition, as pressure increases, more flex occurs in the steel of the barrel breech and receiver - allowing the case to expand a bit more. If chamber pressure is high or the brass relatively soft, the case expands so much that it doesn't undergo enough elastic contraction ("spring back") to allow it to fit easily back into the same chamber in which it was last fired. Without FL sizing, this is not usually a noticeable problem in turnbolts - one simply cranks the big handle a bit harder and the bolt closes. In a straight-pull, the operating mechanism has to redirect the applied force 90 degrees via a cam arrangement considerably closer to the bolt's axis than the turnbolt's knob. Consequently, the straight-pull will not easily close (or open) on a tight case that would hardly be noticed in a turnbolt action.

Depending on the case metallurgy and internal configuration, the chamber pressure at which 7.5 Swiss brass expands enough to get sticky is usually somewhere above about 40,000 psi. Use mild loads that fall below this level and neck-sizing is practical indefinitely. With somewhat stiffer loads, cumulative expansion may mean neck-sized cases stick after several reloads. At full power (normally stated as ~46,000 radial copper crusher or ~55,000 psi CIP/piezo) one or two firings can leave normal cases expanded too much for reliable chambering or extraction without FL sizing.

A seldom-recognized factor is that some seater dies, designed for the 1911 chamber, are too narrow-bodied to admit neck-sized cases fired in a K31 chamber. During seating, such dies compress the case body and displace the shoulder forward, making chambering impossible.



So, one answer to the original question here is - "It depends (on several factors, some of which we can't readily control)". My response, however, is, "What do we gain by neck-sizing for a relatively light-barreled battle rifle?" If we adjust FL dies to produce minimal cartridge end-play, accuracy and case-life will not be significantly different than with conventionally* neck-sized brass - and bolt operation will not be a problem.

*Work-hardening of necks occurs at the same rate with FL and conventional neck-only dies. Collet or bushing-style neck-sizing dies can reduce this, resulting in less-frequent need for neck annealing. Because FL sizing compresses the case body, more elongation occurs during sizing than with neck-sizing - so less trimming is required. For me, neither trimming nor annealing are particularly onerous tasks.
 

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Parashooter,
Thanks for taking the time to provide a very clear and detailed explanation. I think I'll try adjusting my FL dies to this effect.
Pat
 

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Very good answer Parashooter.

I fire one of my K31's in our local monthly High Power matches and have approximately 100 Prvi cases that I have been loading once a month since February 2009 for these matches. Since then, they have never been full-length sized. Granted, I do shoot a relatively light cast load, but they chamber flawlessly every time.
I use a Lee collet die for the sizing operation, and an RCBS die for seating. I have had no trouble with the seating die as Parashooter described in his post. I recently completed a 600 yd. target here at the house and as such have been firing near full power jacketed loads. I find it necessary to full length size these cases.
Really, for informal shooting and even competing on the 100 yd. reduced course I see absolutely no reason to fire full power jacketed loads when reduced loads are:
1) every bit as accurate as full power loads
2) will poke a hole in a paper target just as effectively as full power loads
3) are easier on brass as cases can be neck-sized thus reducing case loss
4) infinitely easier on your barrel

Regards,
35W
4)
 

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I exclusively neck size my 7.5x55 Norma brass and keep my loads moderate simply because I want longer case life and less wear and tear on the rifle. I did make up some hunting rounds several years back that run near max load. I think I still have about 45 left. I doubt I'll ever fire these enough to require the FL sizing mentioned. I will say that this is the first sensible explanation I have read on the subject of neck sizing 7.5x55 though...
 
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