If you are new to pistol shooting and want to get some trigger time do not worry about the 115gr vs. 124 gr issue. As you are just starting you won't be able to tell the diference, nor will you care if there is any. When I started shooting pistols I bought the chepest ammo from W-mart so I was shooting a mixture of 115gr and124gr and maybe even 147gr (often from the same mag) by various manufacturers, including PMC.
The important advice, though, is to save your brass. Before you know it you'll be looking at reloading equipment, and starting with a nice stash of 1000 once-fired cases will get you a good start.