Well I have been working on my stubby m4 it's gone through a few variations now but this is getting closer to final;)
So it started as a Black Ops Stubby that I got for cheap, ran good until I fed it an 11.1v lipo for quite a while. Then the electric blow back was giving me issues with the higher ROF and I stripped the stock piston. So I tore it down reshimmed, replaced the piston and just generally cleaned everything up inside. Tore out the EBB stuff so that it's now mostly a standard gearbox.
Then I got the new stock, so I pulled the front end down, removed the integral suppressor cut the outer barrel down, fit a flash hider(the suppressor is still able to go back on over the flash hider). Cut down and recrowned the inner barrel. Then installed the new stock which is a side folding LR300 stock, took one of my stick lipo's and molded up a kydex cover for over the battery in the stock. And temporarily I went ahead and used some range bands to keep the two halves together. Eventually I'll get around to drilling and mounting them with chicago screws through and maybe some other things. I'm not thrilled with the wire routing but it works, same with the kydex. I can clean it up another day though I was short time and wanted to make it functional for the time being.
Overall works well, reliable and best of all very very short. It's slightly less accurate with the shorter barrel, groups are a little bigger, could be the barrel though since I cut down another one I had around rather than the stock one. FPS might have dropped a little bit but I don't have a chrono right now so hard to tell. Still can hit a target regularly at 50 yards and that's good enough for the plan I had for this gun;)