Modified from a bomber's tail gun?! What was the point of expending fuel to launch such a heavy thing into orbit? The Soviet space program lost its mind after the US beat them to the Moon.
There is a gun onboard the ISS.
A gun port, but not an actual gun, AFAIK.
Soyuz crafts contain a survival kit that includes a handgun, but it's not easily accessible until landing.
They've supposedly stopped in recent years;
https://spectrum.ieee.org/tech-talk/aerospace/space-flight/h...
[1] https://en.wikipedia.org/wiki/Almaz