Please post photos of the proofmarks and numbers you find under the barrel! The mark "2,5gGBlP" = 2.5 gramm (military)rifle flake powder gives the standard charge for the smokeless 8x57 load. As this mark was only used up to 1912, it probably indicates an I = .318" bullet bore. You will probably find the following proofmarks under the barrel: a big crown, a small crown over N indicating nitro proof using the 4000at special proof powder, and the gauge number 172,28. Only if the gauge number is 156,14 it may be a S =.323" barrel.