If you configure your M16A2 to use the following:

Barrel - 10.5" Commando Barrel,
Handguard - FPW Handguard,
Lower Receiver - FPW Package,
Stock - Buffer Tube,
Magazine - 100-Round C-Mag,

Then your gun will use all the ammunition you currently have instead of the maximum amount the magazine can hold, basically infinite if you have thousands rounds on you.

I have tested to see if its caused by other addons that may have likely conflicted with this addon by disabling all except ArcCW weapon.

I have tested other parts as well, only if any of the above attachment is not exactly the same as what I listed, even if you have the 100 C-Mag, then it'll use the 100 limit instead. Other attachment will not affect the result.

This configuration is exactly the same as The Patriot from Metal Gear series.