What is the standard rifle of the US army m16a4 or m4a1 ?

Hello again troll....

The M-16 has been around in one variation or another for over 40 years. Not bad for a rifle that was so soundly criticized when it was first adopted. That's a long time, and it has been used that long for good reason. It is dependable, accurate, and very adaptable to different combat situations and requirements. An M4 is a M-16, in an 'urban combat' adaptation. No the Army will not switch to a new rifle just because there is a war. They may adapt the M-16 to another form (i.e. the M-4) but as I said .... over 40 years and still going strong. Why would anyone feel the need to fix something that isn't broken? Now, they may supplement it with other weapons ... but that doesn't mean they switch. Who really knows what the future will bring? The Army will use whatever they feel will accomplish the mission.

Both, they're in the same family.