For critical safety information, on this round, refer to the article: https://support.leeprecision.net/en/knowledgebase/article/7-5-x-55-swiss. Those who find that discussion confusing are welcome to visit the Internet where the discussions are more complete and equally far more confusing. I must admit I remain concerningly confused! The important points are: The older-model guns have a slightly different chamber The older guns also work at significantly lower pressure The modern 7.5×55 Swiss chambering and associated Military loads have a seriously storied history. The standard Swiss WW-II Military load used a bullet that was so efficient the U. S. adopted it for use in its anti-aircraft and armor piercing 30-06 rounds. Then, it had to discontinue that loading after discovering the bullet was so efficient it would shoot off most, if not all, Military rifle ranges! This case was the progenitor of the 284 Winchester. Running 284 cases through the 7.5×55 die results in entirely functional 7.5×55 cases, despite the 0.027-inch difference in rim diameter. Ballistically, in the more modern rifles, the 7.5×55 comes close to duplicating 30-06 performance, which is no faint praise.

Cases produced under the C.I.P. standard labeled 7.5x55 GP31 do have a slightly modified shoulder angle. The body to shoulder intersection is .002 inch longer on the 7.5x55 Schweiz. Ordonnanz cartridge and the neck to shoulder intersection is .013 inch longer. The headspace datum dimension on the GP31 standard is 1.824 at .375 inch verses 1.832 at .375 inch. The shoulder angle on the 7.5x55 is 27.57 verses 30.46 on the GP 31. Lee dies are manufactured to produce a shoulder angle of 27.57 degrees and a headspace datum of 1.832. This produces ammunition that is safe in a GP31 variant chamber dimension and at maximum material condition a shoulder crush fit of .008 inch would occur. This could cause difficult bolt closing and a no fire condition, but would never produce a cartridge with excessive headspace. We have produced more than 28,000 7.5 Swiss full length die sets since 1995 using the above dimensions, and have had little or no trouble with chambering or proper function. If a user should encounter a chambering problem, the headspace is adjustable by a quick die modification. This would not be the case if we were to produce the die to the GP31 variant standard, cases would be produced that would cause excess headspace in the 7.5x55 Swiss. The above said 7.5x55 K31, Suisse and GP31 variants can be successfully and safely loaded with standard Lee 7.5X55 Swiss full length sizing dies. Be sure die contacts shell holder when sizing.