When I bought the Kurz along with my Aug I wanted it to be my secondary side arm \ CQB weapon.
To make a long story short, I wasn't satisfied, so i decided to upgrade it a bit.
First of all, I wanted a 330 fps weapon, not a 215 one, in order to do so I swapped into a longer barrel (30 cm instead of the 11cm) and also replaced the cylinder to fit the new barrel length.
I also replaced the bushings to guarder metal bushings, a CA 100 m\s spring and covered the new inner barrel with old, china made AK 47 outer barrel. I got my 330 fps but it looked strange.
The next thing was to install a CA M4 \ M15 retractable stock, which is a very easy upgrade that contributes to the aiming and the over all look.
I tried it a couple of times and decided that a change of battery is a must. So instead of the 8.4 V, 600 mAh battery I took an 9.6 v 1700 mAh one, which was a bit big to fit into the battery place inside the K, it needed to be split and rewired.
By that time I got that M203 crave again, so I ordered a RIS from UNC and bought myself a CA M203.
The outer stick as you can see was placed into plastic tubing, later on I changed it's position and made it removable with RIS adapter.
Finally, yesterday I got my RIS in the mail, here is the final look (for now) of my MP5.4K
It shots 15 rps at 330 fps.
Omer