the last RWS made FMJ bullet was infamous for the thin jacket and the bad effect on big game. I am sure woodleigh and the belgian bullets by wim degol are much better.
there is no doubt the original 10,75x63 was only extended by 5 mm to get 0,2 gramm powder more into the case and give the bullet 30 m/sec more muzzle energy. why they did this and why they were believing this was a good idea is something we can't explain anymore. for me its enough to know how to distinghish them and what happen when.