I have been running a 20# Wolff spring and guide rod with my mag-na-ported 6" KKM. I would ocassionally get a ftf at the end of a magazine shooting my reloads of 200 grn XTP's at 1,290 fps. I thought that a stronger mag spring might resolve this issue but that turned out not to be the case (no, I don't limp wrist). So I got to thinking that the ported barrel's marginal recoil dampening effect didn't match well with the 20# spring, so I bumped it down to a 19# Wolff. And while I was at it I went ahead and buffed out the feed ramp, chamber face and chamber using a dremel buffing wheel with auto polishing compound (the small dremel buffing donuts are a perfect match to the 10mm chamber). Without much time and effort I managed to put a mirror finish on the feed ramp and chamber face. Long story short.... she now runs 100%
I've read where some G-20 users were having ftf issues as well and thought that my experience with this problem may be of some benefit. I'm not sure which step was the solution, perhaps a combination of all of the above.