Kiwi,
Give the 10gram bullet a try.It is highly likely that Krieghof didn't mount the scope, but maybe used the 6gram bullet with open sights.If the original owner intended to hunt game larger than Reh(Roe), he very likely had the scope mounted to shoot the 10 gram bullet.S&B ammo may be avaliable with this bullet weight.
rtenenbrown,
It seems that shimming under the rear would make it shoot even higher.
Mike