I've been loading and shooting 40 S&W for a several years while shooting USPSA. I have used Hodgdon Titegroup for the past few years with good results and no 'Ka-booms', which can, and do happen, if you're not aware of a couple important details.
The 40 is a high pressure case. No matter what the old rap says about the 40being 'short and weak', it isn't. It's important to have a very firm taper crimp (but don't distort the case - just firm). I've read some data that showed the CUP pressure doubled by a bullet being pushed into the case .010" during the feed cycle. This is why most guys run 40 a little long in IPSC pistols. It gives you a little safety margin with the right powder. And powder, and its burn rate, is extremely important. In the early days of USPSA limited class using 40, a lot of guys loaded very fast powder (Hodgdon Clays being the most noted - I've had a friend do it with Red Dot too) over a 200 or 220 grain bullet to reduce recoil (it makes the pistol feel like it shoots 'softer'). A lot of guys blew the case head of the cartridge, cracking frames, slides, barrels, and generally scaring the s*&t out of themselves. At this point a lot of people started loading 40 really long (1.220-1.200 oal; Winchester says max oal is 1.135) as protection against bullet setback, over-pressure, and 'Ka-booms' - with mixed results. So all-in-all this doesn't do you much good if you want to load for a standard pistol and chamber (glock, sig, etc.). So what do you use?
Use a powder recommended by the manufacturer for 40S&W and most importantly, for the velocity range you're looking to use it within. The reason I use Titegroup is because I can load it mild to wild at 'standard OAL' over a 180 grain bullet with no signs of pressure. I've used Winchester Super Target for light loads, but it tops out just below the velocity range I normally load in. I can, and have, loaded it above recommended max load but the more I learned about 40, the less I experimented around the edges. Hodgdon Clays is another good light load powder, and there are others. There are powders out there that really push light bullets (read: fast velocity), safely. Read the manufactures web sites, it's all there.
If you've loaded a lot of 45, just be aware that the internal case pressure of the 40 is much higher than a 45 and treat it with the respect it deserves. I've only had one problem with a 40, a double charge using Winchester Action Pistol ( which I liked - but was discontinued), and the damage to the pistol was impressive. Fortunately for me, the only damage was the pistol.
Please don't be put off by the above. The 40 is a great cartridge with a lot of flexibility. You can load bullets from 135 to 200 grains safely, and I've loaded them all. It's probably one of the most flexible auto pistol cartridges you can find. I've shot plates, IPSC, IDPA, 3 gun, pins, even PPC with it. For more info, go to Brianenos.com, there is tons of info on 40 and reloading it.