115, 124, and 147gr. Who, what, where? It seems 115 is most common, 147 some of it subsonic, and 124 I still do not know what it is especially for. Anyone want to explain this, that would be helpful.

Well, this is what I know.

115 is the lightest round 9mm comes in. For defense, I think it is too light of a round. Most police agencies that use the 9 have gotten away from 115 gr rounds. I think all are supersonic - would be stupid if they wern't b/c the bullet is so light. I use these (Winchester White Box from Wal Mart) for practice.

124/127 - a little heavier, still supersonic. I lot of them come in higher pressure, +p, or +p+. I carry Winchester Ranger 127 gr +p+. Speer makes a really good 124 gr +p JHP. Probably, the most common 9mm defense round - A lot of police departments use these rounds. They've proven to be very effective in a JHP.

147 - some are supersonic, most I've seen are subsonic. I have heard that there tend to be overpenetration problems with both, even in JHP.

http://www.firearmstactical.com/ammo_data/9mm.htm

Hope that helps some.

115 offers the least recoil?

I have also seen 158 grain subsonic 9mm ammo advertised, but have never purchased/shot any and have no idea how it might perform.  Just an FYI.

www.natchezss.com/ammo.cfm?contentID=productDetail&prodID=ARA9107&CFID=1007983&CFTOKEN=61872311

9mm comes in a lot more flavors than just three bullet weights!  Federal makes a 135 grain Personal Defense load.  JHPs as light as 90 grains can be found, and subsonic 158 grains are around.  Toss in exotics such as RBCD and Glaser, many super-lightweights exist.

For even more fun, try to make a complete list of all the cartridges that use roughly a 9mm (.355") bullet!