We had about 400 SPS gun toting troops, each with an assigned rifle. Most were M-16A1s but about 25 were GAU-5, GAU-5A, and GAU-5AA. This was late 1980s/1990 with budget cuts rampant and not even money for toilet paper in the latrines. The CATM guys were scrounging parts from any source they could find, including Army rejects from Vietnam. We were still using S&W .38 revolvers. Almost every GAU was a different configuration, some so worn the receivers were 90% bare aluminum. They kept the 6” moderators on the really short barrel rifles to cut down the muzzle flash. We had a number of different qualification courses, including a night one. My first GAU had an extremely short barrel and A1 hider, and after a few rounds my night vision was so deteriorated from the fireballs I couldn't even see my target. The small size was a big advantage, especially for me, getting in/out of a vehicle 10-15 times a shift, and it helped when trying to sneak up on the troops to spring a surprise exercise.
I don't think CATM cared what the ATF thought. They were all full auto guns and we were SAC during the cold war. Use of force/deadly force rules were pretty broad. Any incident with a “priority-A resource” was justification for deadly force. We didn't allow anyone to screw with us and we routinely screwed with every govt agency that tried. We wouldn't Fed LE on the base without good reason and had an armed escort that followed them. If they were FBI and violated our rules, they got jacked up same as everyone else.
I carried my GAU slung behind my back, muzzle down, and it was small enough that the only part people in front of me saw was the sling, which they didn't see as threatening. Some of them got quite a surprise when I whipped it around and suddenly there was a compact machine gun pointed in their direction. I developed a quick-draw technique to reach behind with my right hand, grab the pistol grip, and swing it out in front pointing at the bad guy in one second. I'd sometimes get called to the main gate because some asshole O-5 wanted to give my A1C some crap. Those times I'd flaunt the weapon, and I carried two sets of exposed handcuffs on the front of my web gear. Instant attitude adjustment. We had a reporter trying to film bombers from the perimeter fence. I pulled up in my Blazer, whipped out the GAU, and watched him race back to his car and spin the tires trying to leave. As a 1LT, I could walk into Wing BattleStaff during an ORI, full of O-5s and O-6s, lay my rifle on the table, and instantly be treated with courtesy and respect. They would share stories and laugh about all the other colonels they fucked with.
Despite us being short on quality weapons, there were four big piles of discarded weapons and ammo buried on the base. After a few years, the topsoil eroded away enough to show barrels sticking out. I poked through one and found lots of greasegun and M-1 carbine parts and ammo. Mags that were still in their wrappers, tons of .45 ammo. Stuff from WW2 and Korea. The cheapest way to get rid of it was to dump it, same as massive amounts of hazardous waste all over the base.