I bought a pretty good used one last month for a couple of hundred bucks. The guy was moving to the UK to do Executive Security so he was dumping a lot of things & I've always loved the H&K MP5. I found an in-depth article about modifications to the fire control unit but I keep seeing references to a Navy version of the FCU. What makes it better & if it is, where would I look for one? I've torn mine completely down and I mean to the teensy little springs. I don't think I'll have too much trouble putting it back together but would like to know if you modded yours to make it fire better, etc. I bought a Rrages bolt/nut conversion kit & it already had the HK push pins in it. Now to make some changes as shown in this article.