Hi ira scott
Your Gew 88/05 has been modified for the S cartridge and charger loading.
Your rifle has been altered to use the WW1 S cartridge..
For German military rifles in 8mm there is only one bore size, 7.9mm or 0.311 inches
There were two grove depths, the original at 0.1mm, and the later one of 0.15mm
Original 1888 Barrel =
((0.1mm)+(7.9mm)+(0.1mm)) = 8.1mm = 0.3188976 inches or ~ 0.319 inches
Barrels after July, 7 1896 =
((0.15mm)+(7.9mm)+(0.15mm)) = 8.2mm = 0.3228346 inches or ~ 0.323 inches
S bullet diameter = 8.22mm = 0.323622 inches or ~ 0.324 inches
S and sS cartridges.
With the adoption of the S cartridge, the chambers were opened up to accept the larger neck diameter caused by the larger .0324 inch bullet.
Cartridge Charge Bullet form Bullet weight Velocity (Vo)
S= 98 = 3.2 g = short concave arched base = 10.2 grams = 895 m/s = 2936 ft/sec
sS = 98 = 2.85 grams = long torpedo shape = 12.8 grams = 785 m/s = 2575 ft/sec
Barrel lengths, 740mm = 29.13inches
The sS cartridge was adopted in 1918 as a long range machine gun cartridge and was the standard issue cartridge of WW2.
MARKINGS
2mm diameter dot = Modified barrel contours, post 1891.
Z 3mm high = Deepened rifling groves, post 1896. A large 7mm Z, may also be stamped on the right side of the butt.
S 3mm high = Rifles suitable altered for S-Munition. 1903-5. An additional 7mm crowned S may be found on the right side of the butt.
n 2mm high = Signifies an 88/14 conversion, 1914-15.
Unit marking are generally located on the left side of the barrel band, and occasionally on the top service of the butt plate. For example ( 132.R.5.116 )
The preceding information was from, German Military Rifles and Machine Pistols 1871 to 1945.
By Hans Dieter Gotz. Translated by Dr. Edward Force, CCSU. Includes information on assault rifles and Sten copies.