reloads

Hi Guys, I have loaded thousands of plated 115 grain plated round nose Berry and Ranier for 9mm with .37 CC Lee autodisk that produces charges 4.0 to 4.4 grains of Tite Group and they all shot well from 3 different Kahrs, XD, Sig, Ruger, everything I own. My press is set up to seat the bullets...

I was thinking about getting a SS guide rod for my SD9 and the come with springs 16lb,19 and 21lb. Galloway said that the S&W SD9 comes with a 16lb, but that19lb would be the upper limit. Is the different poundage to accommodate hot loads or light loads? The 16lb factory spring comes with both...