ETR3(SS) did a really nice tutorial on how to tweak the guns. Mostly about adding and/or moving them, but also, it's really helpful at explaining SH's file structure (where to find things and what to change), tools required, and general procedures to get started modding. It can be found here: (if I'm doing this right)
http://www.subsim.com/radioroom/show...=162021&page=2
Basically, You just need to change the "reload time = " value in your gun's .sim file. Good luck
Edit: Looks like he beat me to it.

Thanks again, ETR3(SS). Your tutorial rocks!