These are actually "Short Rifles" ( ie, Musketoons) and NOT "Carbines".
There are three origins for them:
1. German Wholesalers (ALFA, AKAH) had some made from Gew88 (unconverted) in the early 1900s for sale in Export trade...they are usually listed as "Imitation" (of the original Military issue), and may have used non-accepted parts (ie, Serviceable, butm slightly out of spec).
2. Turkish conversion, 1920s (both Gew88 and Gew88/05) . The Turks came out of WW I and the War of Independance/Civil War/ greek War with loads of gew88s in Poor condition (no bolts, damaged jackets, etc) as well as having lost a lot of its original Mauser Carbines/short rifles. They immediately made up the shortfall by "repairing" these damaged rifles into "Short rifles" main indicator is a Turkish (arabic )script serial number, and a "z" marked bolt ( Brno supplied).
3. Your old American Faker... cutting down either Turkish or Equadorean Gew88s into "carbines" ( when actually they are Short rifles ( postion of sling swivels gives the game away.)
BTW, if the item has Long or shortened Long rear sights, it is Turkish or Equadorean;( or Fake); if it has replaced Carbine type sights, then it is a German Wholesaler conversion.
Take a good look at the item. The Turks (and the Wholesaler Models ) are relatively uncommon; Bubbas/fakes are more common...at least in the USA.
Bubbas well done and Turks are difficult to distinguish. (Normal Turk Gew88/05 don't have any Turkish Numbers except on the Bolt and rear sights...they retained their original German serials.