Alan,
I experimented with 19 vs 21# mainsprings in two 5" 1911's (Kimber and Wilson). At most the change in trigger pull was maybe 1/4 lb, measured with Lyman digital trigger gauge. No siginificant difference that I could feel in smoothness, drag, etc. The most effective change to 1911 trigger pull weight is by bending the left and middle forks of sear spring under grip safety. Care must be taken to avoid hammer drop to half cock and/or full auto firing. There are tests/precautions for these events.
WHile altering springs may make a slight difference to trigger weight the best way to improve the trigger on a 1911 is by CAREFUL stoning of the sear and engagement surfaces. Also stoning and smoothing of the ways in the frame that the trigger passes through will often make a noticeable difference in the pull. A silky slick 4# trigger is IMHO superior to a crunchy 2# trigger any day. This can be done relatively easily with a properly sized stone from brownells.YMMV
