For those with Kahr 8-round 9mm magazines who would like them to be 9-round magazines, so you can carry 10 rounds including one in the chamber, I have tested a solution successfully (so far).

First, what didn't work: I tried the Kahr 7-round mag spring and couldn't fit 9 rounds in the mag. Possibly, a less bulky follower might allow it, but I can't speak for the spring force for the last round.

Using the MagGuts 6-round to 7-round conversion for the CM9 & it's brethren, I installed that whole kit in the 8-round mag, with the MagGuts follower and Kahr plastic base plate and plastic insert between the base plate and spring. Testing started with snap caps to see if it had enough force to load the last round, and it did. So I took some S&B 115gr FMJ, some Hornady Critical Defense, and Hornady Critical Duty to the range and tried it. I fired a total of 90 rounds in the magazine filled with 9 rounds each time, and experience ZERO failures to feed.