Just out of curiosity I went out yesterday and tried an 11#. Out of 6 rounds fired two failed to go completely into battery causing a very light and slightly off center striker ding. I re chambered the rounds and they fired after ensuring the slide was completely forward. Another note the gun seemed to flip slightly more than the 13# spring, I'm assuming because the spring is to light and the slide is hitting. I stopped there and installed the 13# WAY better... the gun returns better and to point of aim faster than the 11# or the original.
hope that helps
