Finally on this I point back to the Magazine. remember the 2007 dust Tests. Where Against XM8, FN Scar, HK416 the M4 suffered the most failures? yeah those tests. Consider
the XM8 used a G36 magazine and did not take any STANAG types. This is a unique magazine common only to the G36 family developed by HK made from a clear polymer
The FN Scar used a proprietary type Steel magazine with a Chrome silicon spring and different follower that fits STANAG wells.
The HK416 uses a Steel magazine that replaced the British L85 rifle magazines and is also STANAG profiled with again stronger spring and different follower and curved profile.
Infact the dust trials the US Army issued a new magazine Spring and follower rebuild ( from black to Green) and then another ( Green to Tan) and then a total replacement ( blue follower tan body) which when tested against commercial products caused both the USMC and USAF to adopt a outside product the Pmag. I mean if this doesn't indicate the problem
I don't know what does.