I'll offer a bit of advice -- the most important thing you can do with a sprite like this is ensure it has enough contrast between its shades that they will all show up on a background as bright as this forum's for example. This goes double if your game's backgrounds are all dark -- you'll need to be able to tell it's a gun in that sort of setup even moreso. You don't want all the blacks to blend into one another.
Currently, I'm only reading maybe 3-4 shades on this thing zoomed in about 600%. When I'm zoomed out to, say, 200% even I can only read maybe 2 shades, 3 at most -- *if* I'm squinting and looking very hard specifically for the shading. Otherwise, as a regular viewer, I might not see but the black and the light color of the tripod (2 colors).
As said before, the only fix for something like this is to ensure there's enough pixels of varying contrasts to define the form on any background color, light or dark -- and even on a background the exact same colors as the sprite itself!
Take a look at the thread in this section entitled "Tentacle Perspective Conundrum" and see my sprite there of the tentacle dude. That sprite will work on any colored background -- including a background consisting of the *exact* colors in the sprite itself.
The trick is to use the colors in the sprite itself to test its readability on light and dark backgrounds.
Good news though -- the way you did the left-most leg is a great start with this type of shading -- it will work on both a light colored and darker colored BG due to the way you shaded that leg. On the other hand, the gun barrel and other parts of the legs won't be quite so nice. And another added benefit shading your sprites this way is that for very small sprites like this gun, you won't even have to worry about proper lighting anyhow! If you're sprites are readable shape-wise on both extremes (light and dark, and using the same colors of your sprites for the BGs), you're all set. As long as the form looks workable on both, you've got it.
Don't worry about proper shading until you get into sprites that you have actual room to shade -- then look at that tentacle sprite and some of the oldschool SNES sprites like Chrono Trigger's or Illusion of Gaia and see how they manage their shading. They too keep in mind the idea of sprites looking great on both dark and light BGs -- exactly the thing I'm trying to teach you here.
