Hey all! I've decided that I wanted to turn my CA M15A4 into a MK18 Mod 0.5. I have some of the accessories, and am about to purchase the rest (excluding the 553 or SpecterDR or Comp M4). Problem is, my barrel length is completely off. I tried taking off the RIS today, but couldn't. I can remove the bottom part, but cannot even budge the top part, and fear exerting more force in case I break something important. The RIS can stay, but the outer barrel cannot and I need to get the RIS off to get the outer barrel off. Would twisting the barrel nut help with this? I know it has to be loosened for the outer barrel to come off, but even if I bought an armorer's wrench to remove it, I can't use it, because the RIS blocks access to 3/4ths of the ring. It can't be budged right now either If anyone has any experience with taking off the outer barrel and RIS, or just wants to speculate, any and all replies will be appreciated. Thanks!