M6 used by USAF had 14" barrels to fit under the
aircraft ejection seat. The civilian version has 18"
barrels--exactly 18"--for minimum legal shotgun
barrel length and the civilian version has the trigger
guard mandated by the lawyers. The original trigger
(I have always been told) was designed to be fired
while wearing winter mittens.
The M4 survival rifle was a bolt action, box magazine
fed, wire stock, detachable 14" barrel, .22 hornet
issued with FMJ ammo. A few of these were accidentally
released on the surplus market before someone realized the
minimum legal rifle barrel length is 16"
Armalite made a survival rifle for the USAF that was
bolt action, detachable barrel, .22 hornet, and the
parts fit in the stock. It was approved but was never
procured or issued in any significant numbers.
Armalite developed the concept into the AR7 Survival
Rifle for the civilian market, which is .22 LR, semi-auto,
16" barrel. The AR7 has been manufactired over the years
by Armalite, Charter Arms, Survival Arms and currently
(or lastly) by Henry. The oo7 movie From Russia With Love
came out when the rifle was still made by Armalite.
For survival purposes--usually vehicle breakdown in the
boondocks--anything to keep predators at bay, kill
game for food, or just keep one from feeling defenseless
will do. I like a 18.5" barrel, no choke shotgun that will
safely fire 12 ga Marine signal flares as a survival gun.
.