I'm going through this now. 700X is the only fast powder I have (other powder I use lots of is Trail Boss - great in .45 behind a 255gr boolit, but I don't think I can fit very much TB in a 9mm case!)
Boolit is the 120gr Lee TC in a 6-cavity mould. Pistol is SWMBO's H&K P30L - it has polygonal rifling and H&K do not recommend it be used with cast lead, but until jacketed bullets are as cheap as wheelweights, that's what it's getting. I will say from the outset that there has never been any evidence of keyholing with this bullet - everyone has left a nice small round hole, irrespective of how wildly off-aimpoint it is.
My first load for it was 3.8gr 700X - TERRIBLE! The pistol was real loud and gave a very noticeable shockwave; it was clearly well above speed of sound (it's blizzard here and 2 feet of snow, we were on the indoor range in fluorescent light and I didn't bother trying to use the Chrony down there) and the P30L just spat them at the target - at least they were all on-paper, but no evidence of any sort of grouping. I decided to download a LONG way and try again.
I loaded-up three trial loads; 3.3gr, 3.0gr and 2.7gr 700X and we tried again:
1) 3.3gr sprayed boolits as bad as the 3.8gr load, and the pistol would cycle them for me but they started giving "her" problems;
2) 3.0gr sprayed somewhat less - it was starting to group - but the pistol stovepiped all of them for her, and most of them for me; and
3) 2.7gr was good and accurate; a quite satisfying 10-round circle, but the action had to be worked by hand for every round.
So we took it back to the range with commercial ammo; S-B in 115gr and 124gr loads, and a box of Geco 124gr's. It grouped well with them all, and seems to like the 115gr's best; there's nothing wrong with the pistol except that, like H-K says, polygonal rifling and cast lead don't appear to do well together.