Are you using scrub Gen1 mags?
You should look into their newer "Gen 2+ mags"
To be honest, you can file the firing pin to run GHK G5 magazines , which is what you should do.
https://www.youtube.com/watch?v=yw6ZdlxXKUc
But honestly, you'll invest way more then you want to invest, and a out of the box GHK m4 will out shoot it no matter how much you invest in it.
If you want strictly "416" get a WE, and hang your VFC.