After a smart tip bij Chris K (thanks!!)I examined the O-ring on the compression tube cap (nr 5). There were some minor cuts so I replaced it and applied blue loctite to the threads.
Velocity went up by 100 f/s to an average of 902 f/s. Not quite the 940's but maybe my spring suffered a bit from shooting with a leak. Thanks to all who responded to my cry for help. It is much appreciated.
Mark
