My understanding of the Gew.88 is that it is a a .320" bore with a .318" bullet. At that time frame jacketed bullets where new. The jackets where thin. It was thought that the .318" bullet with the soft lead core and thin copper jacket would "slug up" in the .320" bore. A lot of rifeling from that time frame appears to be worn as the lands tend to be rounded. These where purpose made that way because square lands would cut the jacketing causing the bullet to come apart.

I have multiple Gew.88 rifles, carbines and Gew.88 based sporting rifles. Most of the sporting rifles where purpose made and not converted from military rifles. I have not slugged all of the bores. Some of those I have are a Haenel model 1888 sporting rifle, lands are .311" and grooves are .321".

Hanel #1 Mannlicehr-Hanel sporting rifle, lands are .305", grooves are .316".

Hanel #1 Mannlicehr-Hanel sporting rifle, lands are ..310, grooves are .318".

Hubertus Model 88 sporting rifle, lands are .309", grooves are .320"

Eduard Kettner Model 88 sporting rifle, lands are .303", grooves are .314".

Haenel Kar.88, lands are .312", grooves are .319".

Haenel Kar.88, lands are .313", grooves are .319"

Gew.88 based sporting rifle, lands are .311", grooves are .319".

It seems that the military barrels tend to be .319" or larger and the sporting rifles are using much tighter bores possibly with the idea of boosting velocity by increasing pressure.

Vlad