5.56 Magazine or Manually insert round?

[cwlongshot]

I haven't had too but,...I believe there a couple threads on people using 5.56 magpul mags you can only load 3-5 rounds before it causes the mag to swell. Going off memory here but do a forum search. I would do this before single loading in chamber this is usually what causes the rare instances of that free floating firing pin to slam fire.

Exactly, a 223/556 mag usually works perfectly BUT you cannonly load a few cartridages. See its the larger dia or the Grendel combined with the way the follower tries to push the cartridages.

On my first build correct mags where difficult to obtain. I sited and hunted with magpuls using four rounds and the gun ran flawlessly but try 6-7 and it was a NO GO! It isnt ideal but just load 3-4 and you should be able to site and shoot till your correct mags show up!