The ACR AVe-CoR(pronounced ave-core) is used by most of the US military branches, as well as many governments around the world. It is able to utilize a variety of ammunition, rail systems make custimaztion easy, and interchangeable barrels make this the most veristle rifle ever built. It can be modified to suit all your needs, CQC combat or long range sniping.
The M5A3 is the new upgraded version of the M4A1. Using G36 German rounds and a detachable suppressor. This is new generation of warfare. Has been built to be in the water and in any climate imaginable. This will change the tide of a war.