The M16 has been in service for over 40 years and I did some research to see which governments now use it. I decided to create a map showing who uses the M16/M4, AR-15 (civilian version)and the C7/ C8 (Canadian version).
This is what I came up with (click the image to increase the size)
Some of the countries, such as the UK, only use M16/M4/AR-15/C7/C8 rifles for their special forces. Presumably because the AR-15 platform has no end of customizations available.
Here is a complete list of countries (from the Colt website. The above map is more detailed than the Colt map):
Argentina, Australia, The Bahamas, Bahrain, Barbados, Belize, Bolivia, Botswana, Bosnia and Hercegovina, Brazil, Brunei, Burma, Cambodia, Cameroon, Canada, Chile, Colombia, Congo, Costa Rica, Denmark, Dominican Republic, Egypt, East Timor, Estonia, Fiji, France, Germany, Ghana, Greece, Grenada, Haiti, Honduras, India, Indonesia, Iran, Iraq ,Ireland, Israel, Japan, Jordan, Jamaica, Kuwait, Lebanon, Lesotho, Liberia, Maldives, Malaysia, Mexico, Morocco, Nepal, New Zealand, Norway, Laos, Nigeria, Netherlands, Oman,Pakistan, Panama, Philippines, Portugal, Qatar, Saudi Arabia, Singapore, South Korea, Spain, Sri Lanka, Taiwan, Thailand, Tunisia, Turkey, United Arab Emirates, United Kingdom, Uruguay, Vietnam and Venezuela.