RWS say in his Reloading Manual about 600m/s ( 1950fps ) but you have to use very fast burning powder because the small capacity case! The ballistic is very poor! I never try to do that, the original bullet is the 347gr. thin jacketed FMJ bullet, very difficult to get today! And the next problem is the diameter of this one, between 10,70 and 10,73 ( and sometimes more ). The original 10,75x68 is different when you compare to the 404 Jeffery! Today a lot of "modern" 10,75x68 rifle's have a 404 ( .422 ) barrel!

For information:

404 Jeffery / 10,75x73 grooves 10,41 / 10,62
10,75x68 grooves 10,45 / 10,75