Here is a good quote that might help.
There was quite a lengthy conversation/debate on the old forum.
"Since the questions always come when someone is trying to shoot their Gew-88, I would call it more mechanical than linguistic. If they are going to be shooting the rifle, they should know the safe way to do it. The .318 bore myth is the first problem and is compounded by the "S" means it is a .323 bore. Those can cause problems that are dangerous as saftey issues, or just spending alot of extra money to make incorrect, poorly performing ammo. The original German bores were not .318 groove, just the bullet was .3188. So when people are told to buy .318 bullets, they are wasting their money. The "S" stamp is not a bore size, it does not mean the throats were lenghtened. The original p-88 ammo needed atleast .666 clearance from the case neck to the land to clear, the later "S" ammo only needs .315 . The main body of the "S" bullet is .321, the original groove is .321, so they fit and do not need to squeeze anything. The OD of the case neck on original P-88 ammo is from .346 to .348 and on original "S" ammo it is from .348 to .350. Most military chambers are over sized, my G-88's chamber neck ID is an average .354, my Gew-98's are .360 . The "S" stamp means the original G-88's neck ID was checked and if it was by chance on the extra small side it was neck reamed to clear the .002 extra ammo neck dia. That is why most G-88s rifles still have the old P-88 sight on them, they were just cleared to fire "S" ammo if needed. There was another "S" stamp [ rare ] if the rifle was also sighted for the "S" ammo. The South American import G-88's still show the "S" stamp, but many have Czech barrels that are as small as .306- .316. People are still being told they can shoot .323 bullets in those. So that "S" means nothing now. The Czech barrels are the same size as German civilian barrels, too small for the .3188 dia military ammo. The German civilian ammo has a .316 dai bullet , as does the Czech military ammo. So a .318 bullet is not correct for most Czech barrels either. Since most "S" stamped rifles had nothing changed, it is not a "conversion" of anything. The '05 update was a conversion, as the magazine loading was changed to stripper clips. The notch was not cut for the "longer" "S" ammo as the "S" round is only 3.17 long compared to the P-88 round's 3.24. If you put a tape block across the notch and then Correctly load a clip full of "S" ammo you will see there is still .10 clearance between the tape and bullet. The distance from the rear of the guide and the top of the receiver if there was NO notch is 3.30, the "S" ammo in a stripper is only 3.20 long, there is extra room. The over hang of a partialy inserted stripper does not matter as the ammo will follow the clip back to the rear of the guide. If you load a stripper full of the older P-88 ammo you will see that the notch is a guide for the P-88 bullet tip, it fits perfectly and it is tapered to guide the round nose bullet. Plus the extra space of the notch is needed as the P-88 ammo in the clip is 3.38 long. The "Z" was not really a conversion, just the next bore size on new made rifles after 1896+. A change, but not a conversion. When older rifles were rebarreled after 1896 , they got the "now in use" barrel. It was not a conversion to those either as ONLY repaired rifles got them, if the old .321 barrel was still good it stayed. With ORIGINAL barrels the bores sizes where: 1889 to mid 1890- .314 - .3215 ,,, Mid 1890 to mid 1896 .311 - .3215 ,, Mid 1896 to end - .311 - .323+ . What I have said here matches everyone of the 100's of G-88's I have checked, I have never seen one that does not, so I am sure it will be true for a rifle someone else is trying to shoot. BUT THEY STILL NEED TO SLUG THEIR BORE to see what barrel they HAVE, and not go by what they have been told, there a a few shooting "websites" that are telling people .318 or "S" = .323 and to shoot that without checking. Everything I have said can be checked if you have a rifle, ammo, clips. mag"
