Algodoo

Neat little concept i came up during class to simulate a gas piston without any gas.
You can use the keyboard to manipulate the firearm, the controls are shown on a text box in the scene.

The controls are as follows:

Shift to operate the charging handle
Enter to pull the trigger
Up arrow key to switch to safe
Down arrow key to switch to full auto (as i did not make a semi-auto version... Yet? Maybe.)
E to eject the loaded magazine
X to remove all aesthetic parts, in case you wanted to have a gander at the insides

...

Now it's time to yap.

Uses the spring constant from the fired bullet to push a piston to the front of the piston tube and uses the intertia from said piston to cycle the firearm.
Short-stroke piston shamelessly redesigned from the FN FAL 50.00 and mocked up to look like an AK since those are my one true love, this ended up making it look more like a Saiga-12, if anything. Overall i am quite happy with how this one turned out, since i don't pay attention to any aesthetics and i find beauty in the mechanical bits and pieces.

Much love from Kilo, have a nice rest of your day.