The K31 has a little different specs than the 1911 spec chamber. If you have a K31 and use the standard 7.5x55 die, it will oversize the brass, making the brass fit a little looser and reducing case life. The reason most have the 1911 spec die is the round will fit both chambers, where the true K31 Redding dies will not size the brass enough for the 1911. If you check out the Swiss rifle forums, you will find out so neat stuff about these guns. An afterthought, since you can neck up .284 Winchester brass to work for a 7.5x55 a 30/.284 Winchester reamer might be easier to come by.