I'm in the process of getting age verified, just need the time off work that's reasonable to do so.
Anyways, I'm willing to do my own work. I've always had a knack for tinkering/modding things.
Based on what I've read/seen about the M4 SopmoD, it has an internal battery in the collapsible stock, has rails, blowback, and even a recoil system (which is great for realism).
See this site M4 SopmoD