OTs-12
It’s an AK but chambered in 9x39mm.
Ok, so to properly appreciate what led to the OTs-12 we need to go back a bit.
The original AK-47 was chambered in the (at the time) new and exciting 7.62x39mm round. It was the first successful, true assault rifle and set the standard for decades blah blah blah. It was further developed into the AKM, chambered in the same 7.62, and became even more widely used. 7.62x39 kept the same diameter as the Russians’ earlier 7.62x54mm round but shortened it to make it lighter (so soldiers could carry more ammo) and more controllable (so they could actually hit what they were aiming at).
When the 1970s rolled around, the Soviets took note of the US’ success over the past decade or so in using the 5.56 round - an even smaller caliber, higher velocity bullet let soldiers carry even more ammo and made for even more controllable full auto fire. They decided to match it with their 5.45 and created the AK-74, which (much like the American M16) has soldiered on to this day with only minor changes. Much like the US shortened the M16 to make the M4 carbine, the Russians shortened the AK-74 to make the AKS-74U.
Then we get to the 1990s.
After a few decades of 5.56/5.45 dominance in the world of infantry weapons, people are getting antsy for something new. Not for any real reason, just because they’re bored and need some project to justify their paychecks. In Russian this took the form of finally finishing development of the 9x39mm round (which had technically been around since the 1940s but never really went anywhere). Someone got the idea of taking the AKS-74U and going backwards up the tech tree - re-chambering it from the small and fast 5.45 to the big and slow 9x39. The potential benefits of this new OTs-12 were two-fold: a bigger round would have better penetration through cover, and a slower round is better for sound suppression.
This sounds great, as long as you failed high school physics. The rest of us can immediately see the problem: Kinetic Energy = 0.5 * mass * velocity^2.
Velocity has a much bigger impact on KE than mass, so if you drop velocity even a little bit you need a BIG increase in mass to keep the same KE.
The end result of this is a weapon that works pretty well for a very small subset of missions and is inferior to existing weapons for everything else. You want to storm a building? Great, you’ve got something that hits hard at short ranges and can be suppressed for being all sneaky-breeki. Are there hostages? Sucks to be them, because that extra mass means it’ll go right through the wall and hit whoever is in the next room over!
Actually, considering Russia, that’s probably seen as a feature not a bug.
The OTs-12 never even went into mass production and was replaced by an even goofier AK derivative.
