[300winmag]

Who makes those magazines? Magpull?

The two magazines shown are Lancer and H&K. Magpul would also work, but you have to leave off the top cover. The Magpul also has a "fat floorplate", so you can only insert the bullet end.

Just about any M16 mag, including a 20-rounder, will work, one way or the other.

[osagebowman]

Thanks, that might be handy item to have. Another one goes into the saved pile. :-)