The Gewehr 88 is in essence a Mannlicher design, though it is sometimes (incorrectly) called a "Model 88 Mauser. As such I can't find them in the Mauser Books.
Several thousands of Gewehr 88's were given to Turkey for combat use during WWI. While these were slightly out of date even then, they were useable. The Turks did rebuild most of them in the 30's but some are available in the original configuration with some Turkish markings.
1888: New Bolt action smokeless cartridge rifle adopted by Imperial Germany. Bore diameter, .311, Groove diameter .318. Bullet diameter .318 Bullet was long and cylindrical. Cartridge called "Patrone 7,9mm J" (Infanterie in Fractur script)
Early trials found that the excessive friction of the long cylindrical bullet and identical Bullet-Bore dimensions led to increase risk of split barrels and also excessive metal fouling. Rifling Grooves deepened to .321. This was noted by marking the Barrels "Z" (for "Zuge" meaning modified rifling); at the same time, new steel was adopted for the receiver and barrel ("nm" mark "neue materiel" )
Your barrel was never replaced from the slugging of your bore,and the dimensions you gave. It's not the action that's the problem.It's the barrel.If your going to paper patch I would use a .308 to start. Two wraps.If the Turks rebuilt at that time it is clearly marked on the receiver.Your's shows Turkish ownership,but the date is still 1880 on the receiver.
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--------------------------------AS( )FA-------half-moon ( )
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----------------------------------19XX---year of rebuild 1930 to 1940
Attachment 77479
I have a 1940 rebuild of a mod 93
Attachment 77478
Portuguese Mauser in 8mm (8x57) is the last one
Attachment 77480