The SKS fits your criteria, except that it is not particularly rare. Used in Korea, RVN, & a few smaller conflicts.
Honestly, the SKS may be a perfect choice for this thread. I mean, we as gun owners/enthusiasts are generally familiar with the SKS, but it's nowhere near as "iconic" as AK variants and the AR-15(M4/M16).
As far as practicality... I mean even today, an SKS is a very capable firearm all around. Maybe not so much for combat, given much larger magazines, even at the time they were manufactured, but firing a good round, being accurate enough for combat, or hunting, they are still great.
Although looking back, even when they were adopted by Russia very late in WWII, it was already outdated... Strange, that they'd even consider the thing, but as an alternative to the Mosin-Nagant, PPSh-41 and all the other less known weapons, I'm sure it had it's place. Somewhere.
The only thing I never got about SKS's was like "Does it want to be a Designated Marksman Rifle? Or does it want to be a Battle Rifle? Or maybe something like the role the M1 Carbine had?" I just don't know.