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There is no practical difference in accuracy for the simple reason that a properly-resized cartridge's shoulder cone centers the neck and bullet when it encounters the chamber's shoulder cone, regardless of whether the major diameter of the cartridge shoulder is .454" or .471" (assuming the chamber shoulder is the usual ~.475" found in the K31). Cones are like that - it's basic geometry.

There is also little practical case-life difference. A K31-style FL die works the upper body and shoulder less, but either style works the neck about the same (depending on the dies' neck and expander dimensions) and work-hardened cases normally suffer from neck cracks long before fatigue damages the shoulder and forward body. Annealing the neck and shoulder alleviates work-hardening in both areas.

The K31-specific dies are a little easier on the handloader's muscles and produce less elongation (when used with cases last fired in a K31). To some folks, this is worth the added expense, most of us have no problem with the regular dies and use them to load perfectly suitable ammo for 7.5 Swiss arms from the 1889* through the K31.

*Yes, 1911-style dies work for loading the slightly shorter-necked cartridge used in the pre-1911 models - with appropriate charges in the weaker 1889 and the lightweight 1893 and 1897, of course.
 

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Those who believe that a close-fitting case body makes a significant contribution to K31 accuracy might consider the results normally obtained with GP11 ammunition, which fits the chamber less-closely than ammo reloaded with about any style sizing die. Few of us can improve on it significantly without using best-quality match-grade bullets.

Low-pressure loads that fail to expand the neck/shoulder are one clue that the bullet normally starts to move forward before the case expands (although crimp, neck tension, bullet weight, and several other factors may affect the sequence). It seems to me that presentation of the bullet to the barrel is primarily controlled by the pre-expansion shoulder cone, especially if the case has been sized for minimum end-play.

Many handloaders get carried away with techniques that may produce significant results in a heavy-barrel precision rifle but have no observable effect when we're loading for a lighter-barreled battle rifle. Time, effort, and money is probably better spent on live-fire practice.
 
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