The AMU serves a specific purpose. The others may as well, I am only privy to the AMU's mission. They fall under USREC. Recruting Command. They are part of the PR for the ARMY. Just like the ARMY dragster, NASCAR, the Air Force monster truck and so forth.
They have "train the trainer" programs where they are deployed all over the world training instructors so they can in turn train their troops in the latest marksmenship principles.
The AMU custom firearms shop not only builds and maintaines the firearms to win Olympic Gold, International titles, IPSC trophies and National titles, they do R&D on new weapons systems, developing the next weapon platforms for the future.
I personally know several shooters that joined the ARMY because of the AMU. Some are Rangers and all are superior instructors. One is a girl! We are OK with that. She is
tops! Go Sherri!