M16 magazines in the US military

[Nyles]

I'm not a US soldier so I can't comment on mags, but no way in hell would bringing in their own ammo be allowed. That would NEVER fly in any army. That will get you sent to jail.

As an aside, I don't know why anyone would be willingly using thermold mags. We originally used them with the C7 and they were so terrible we got rid of them in the 90s and bought steel ones. This was a time when the budget was so small there was talk of getting rid of the artillery entirely.