A QUICK WARNING:
For any inexperienced/new reloaders looking at this thread, there is NO published data for this powder with pistol rounds. It's a match-grade shotgun powder. Alliant has expressed their intention to publish pistol data for it in the future, but there's no guarantee that when they do publish data for it that the data will include 9mm. In the meantime, they have suggested Red Dot data minus 10% is a safe place to start.
Remember that if you choose to load with e3, you are in uncharted territory. If you don't have a chrono, don't even think about it. If you do have a chrono, I would personally recommend starting low and working up. Many are looking at 3.0gr as a safe starting load for 124/125gr bullets, and a few tenths lower for heavier bullets. Mining other people's data on the internet will net you other people's higher working loads, but unless you start low and work up with a chrono, you don't really have anything to judge pressure by. And when you're in uncharted territory, don't rely on other people's measuring devices working the same as yours. Start low and work up. Start low and work up.
Also, while I have not experienced this myself (because I haven't gone this far), I have read others discussing getting over-pressure signs in primers at 4.2-4.4 with various 124/125 bullets. This does NOT mean you should consider 4.2gr the upper limit. Over-pressure signs in RIFLE cartridges, IF you have the experience-base to do it, and IF you have a baseline with that powder, primer, case, bullet, and rifle, can let you know you're going too far. That's with rifle. It's not the same with pistol. With pistol, if you get pressure signs, it's a sign you went too far a while ago. Pressure signs at 4.2-4.4 with e3 in 9mm is not indication that 4.2 is the limit. It's an indication that the limit was passed a couple charges ago. Keep that in mind.
You can load 9mm with this powder, but move slowly and be careful.
