[LocoYokoPoco]

So, since no one answered my previous question, I decided to try it out myself...

I've confirmed that aftermarket WE charging handles are not compatible with the KJW M4. However, it looks like with some dremel work and JB Weld, it might just work.

I've also confirmed, King Arms VLTOR Casv rails do fit, but require some pretty permanent modification to the upper receiver. Also, the G&P G27 GBB grip fits perfectly, no mods required, as well as any AEG M4 stocks.