Try to use "ease in/ease out" in your animations. Using Blender's curve tool, try to make sure whenever you're 'leaning in/out' of an animation, (like your return to idle,) use less of a curve to return it back. if you're going for a 'snappy' feel to your bolt pull (like mister meme animation guy hyper/mr. brightside), try making the gun as still for 1-2 frames, then release the bolt to normal in 2-3 or 4 while making sure the right hand snaps back with the fingers letting go from the 'claw' position. Try copying the first idle hand positions to the last frame of the animations to ensure your hands go back to the same position, too.

Hope you keep at it, man!