As promised above, here are the results of velocity testing of this load earlier today - using a Caldwell chronograph:
Shots 1-5 in my CZ 452 long barrelled, respectively: 710FPS, 897, 899, 899, 891. Those last 4 are amazingly consistent, to the point that it's difficult to excuse the first!! That's a massive difference ... and may explain why it printed that inconsistent initial group. For comparison, I also shot a CCI Quiet - recording 650FPS ... which is about correct for this rifle and load.
A massive difference between the two ultra-low loads - an increase of roughly 40% over CCI Quiets ... and easily explains the perceived difference in sound that I spoke about in my first post above.
For further comparison, the ZX's recorded around the 925 FPS in my 20" Lithgow. Again, about correct given the shorter barrel length .... with 20" being usually acknowledged as the "sweet spot" for velocity in the LR loading.
Hope this info helps.