NY -
Walkalong is right.
• .010 to .020" difference in OAL is NOT the end of the world. Now, if we were talking .100" then you'd have a valid point. What we really worry about is beginners who might feel inclined to "load by eyeball" rather than buy a caliper and measure. Since few 9mm bullet have canelures, we really want to encourage newbies to buy calipers at the outset (that is to say, before they blow off their hand), and load to a known OAL.
• You can safely use most any load and OAL you see listed for a jacketed RN 115gr bullet in 9 Luger that specs
your powder. Equivalent jacketed RN bullets would include Remington, Winchester, Speer, Hornady.... well, you get the picture.
• If you feel unsure or simply want to know about the volume in the case below the bullet, then subtract the bullet's length from the OAL and that will tell you where the base of the bullet is sitting relative to the base of the case. This dimension also comes in handy when it comes time to make sure the bullet is not compressing the powder.
• To ensure good feeding, keep your OAL for RN out on the long side. The SAAMI max is 1.169" (or 29.70mm), so stay in the ~1.150" area and you'll do well. (If I remember correctly, the WWB is in this OAL range.) The reason for the 'longer vs. shorter' is how the ammo will sit in the magazine. If the OAL gets too short, say 1.010", one cartridge may sit way forward in the mag, while the very next may sit far to the rear of the mag. The lips of the mag may present the 2 cartridges differently as the slide strips off the next round causing failure-to-feeds. So the longer length helps maintain consistent stacking within, and feeding from, the mag.
• Now then, whatever decisions and calculations you make, be sure and record those in your reloading notebook. After a few reloading/shooting sessions, a clear preference for load and OAL will emerge. Shot groups will shrink. Smiles will emerge.
You're going to love those PD bullets! I've experimented with over 30 different brands and weights since I started reloading for my 9mm CZ. Of all those, the 124gr RN PD is the most accurate of the lot. I love those bullets.
Enjoy!