Actually it did do something - the 98k now has massive damage (last offense level takes only one hit to complete for example), but still - if it unlocked some kind of auto rapid fire it would make this game make a lot more sense. That expert badge for the speed challenge is still impossible..
So I FINALLY got the "Kar 98k Run" achievement, and it unlocked something called "Kar Beast Mode", which you'd THINK might be something that would allow you to do a 3 second speed challenge, but it doesn't seem to do anything!
 "The Gun Game"){kind=icon}