Gerd,
I am happy to add my two cents to the discussion as well.
The cartridge 8x68 needs a long barrel – what a short barrel does to it’s performance can be seen from Rolfs experience.
I achieve 835 m/s (2740 fps) with the 200 grains Speer bullet seated to an OAL of 87,5mm (3,44”) out of my ZG47 BRNO in its factory cambering 8x64 and a heavy load of Vihtavuori N160 together with the 600mm long barrel.
Although this performance is not bad and adequate for most game the user of an 8x68 search for better performance.
Twist
When RWS developed the cartridge in 1937 they tested the regularly twist length of 240mm which is about 9,5” just to find out that the 33,5 mm long H-Mantel bullet weighing 187 grains was not stabilized at the velocity of 1000m/s the 8x68 is capable. Reducing the twist to 280mm (11”) gave the requested stabilization.
Therefore I do not think going back to 9,5” again will be a good idea.
The claimed velocity of 1000m/s (3280 fps) was reached out of a 700mm (27,5”) long test barrel. Internal test shows that a barrel length of 600mm (23,6”) reduce the velocity to 956m/s (3136 fps). It should be noted that this where tight test barrels. (see: Schiesstechnisches Handbuch fuer Jaeger und Schuetzen RWS 1940)
I also believe that the today overall length given by CIP with 87,0mm (3,42”) do not justify the cartridges performance. Original advertisements list the cartridge together with the magnum length Mauser action (see page 173 John Speed The Mauser Archive).
With boat tail long bullets like the 200 grains Nosler Accu Bond even an OAL of 94 mm (3,7”) could be used effectively.
When I decided that I need an 8x68 for my Namibian hunt in the Khomas Hochland, I was influenced by an article of Harald Wolf in his Hatari magazine. He made me aware what is much more important than action/magazine length and that is barrel length! My barrel is 750mm (29,5”) and this gives me about 945m/s or 3100 fps for the 200grains Speer bullet. My action is a modified DWM 1909 action with a new magazine box to accept a cartridge of 87,5mm OAL.
Yes, this is limiting me to some shorter bullets e.g. without plastic tips, but the velocity is limiting me to strong bullets anyhow.
Robert