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.
