“Don’t fuck with the Mormons; they make good guns and aren’t afraid to use them.” — Outlaw saying
Utah is known for three things: Mormons, monsters, and machineguns. (The last two are related.) The best firearms in the Outlaw and the Fed are made in Utah, made in great numbers and at high quality.
The .50 caliber Browning machine gun, standard on most convoys. The .45 Colt 1911A1 pistol. The 7.62mm KBR-22, a modified Type 56 clone (itself a modified clone of the AK-47). The “twin 35’s”, the KB-35 (a KBR rechambered for 10mm ammo) and the CB-35 (a Colt 1911A1, also rechambered for Browning 10mm rounds). An assortment of hunting shotguns, rifles, and bows.
And ammo. Lots and lots of ammo.
The most common firearms in North America are pre-Collapse weapons. At the time of the plague, there were approximately 310 million non-military firearms (civilian-owned, plus local, state, and Federal agency weapons) in the United States. 47% of households owned at least one weapon, and there were 5400 licensed firearms manufacturers.
Second most common are locally produced weapons, of many varieties. Ground out on machine shop benches by individual craftsmen across the continent, these pistols, rifles, and shotguns are of varying quality. They have the benefit of being cheap and locally-made — no need to wait for a convoy, just make it yourself. (Ammo can be a little trickier.)
The third most common weapons in the Outlaw are Browning arms, and the most popular Browning weapon is their clone of the venerable AK-47, the KBR. If there were an official weapon of the Outlaw, the KBR (Kalashnikov-Browning) would be it.
The AK is legendarily rugged and reliable under a wide range of conditions. It can take insane amounts of abuse, up to and including sand in the mechanism, and still operate. AK’s have been fitted with a number of underbarrel accessories, like grenade launchers and shotguns. The rifle is very cheap to make, and can be turned out in large numbers quickly and easily.
Designed by a Soviet gunsmith at the tail end of WWII, the AK became ubiquitous in the Cold War because of its reliability, low cost, and high stopping power and penetration. As Outlaw settlements are about as rich and peaceful as your typical pre-plague Liberian village, the same conditions and qualities that made the AK attractive to Third World nations, also made it attractive to the Outlaw.
But what made it ubiquitous was the Chinese.