First thing...your Gew88 is at least 110 years old, if not older ( production dates, 1889-1897).
Secondly, the barrels were originally made to use a .318 round nose projectile in a .321 Groove barrel
(so called "7,9x57 J");
In 1905, the Germans upgraded to a Pointed bullet of .323 diameter (7,9x57 JS), for the Gew98 (new rifle).
The older Gew88s were then "upgraded" to use the new diameter ammo, by relieving the throat of the rifling to better engage (and swage) the new bullet. Most (but not all) Gew88s received this "s" conversion, and are so marked on the receiver and/or barrel.
This "s" conversion was suitable only for the original 154grain "S" bullet, with a very small groove bearing surface...the Boat tail 198grainer of WW II and later is definitely too long and heavy for use in a Gew88. (pressure risks)
Yugo Milsurp is at the upper limit of pressures for 7,9mm Military ammo, and its age (most Yugo is 1950s-1970s ), is designed for use in "S" type rifles (.323 grooves, M98 type three lug bolt.) The 198 grain Yugo bullet is meant for Kar98k and Yugo M48 type rifles.
The fact that you may have fired some 200 rounds through it means nothing...it will eventually give way, either by cracking the bolt lugs, bulging the chamber, bursting a barrel (common occurence with even the early "J" ammo); Even a simple case failure will send debris and bits of bolt back into your face.
If you want to shoot your Gew88 safely (for the next xx years,), Use either US Commercial "8mm" Loads ( lowpowered and undersized bullets), or handload your own with either case lead bullets (the safest way) or reduced load jacketed bullets ( say 75% powder charge.) by either using new components, or dismantling the Yugo ammo, and re-measuring the Powder charge.
Regards, Doc AV