Actually the "AR" as in AR-15 stands simply for ArmaLite, not ArmaLite Rifle.
The ArmaLite AR-5 was a break open over/under .22 Hornet/.410 shotgun.
There was also an ArmaLite AR-17 that was a 12ga shotgun. http://store.vintagepaperads.com/ser...h-17-12/Detail
That's funny - I always heard that "AR" stood for "American Rifle" and thought it was just a specific series of models at Armalite.
Hmm - you learn something new every day