I like where you are going with this, keep up the good work. So far the sprites look very good.
My one thought though, is I'm not sure if they're quite enough.
For technical writing I learned the "CRAP" principle - Contrast, Repetition, Alignment, Placement. In turn this adds up to "Things that are similar should be very similar, those that are not should be very different."
Especially when working with sprites, the differences need to be very extreme to be noticeable. Take heed of the fact that in vanilla, each class of weapon is an entirely different color. (gunmetal, brown, off-white in vanilla, yellow, silver, red in TFTD).
In this case, for upgraded rifles, give them cammo stocks, sights and under-barrel lasers, and curved magazines (aka "tacti-cool") for enhanced lasers add visible blue coolant hoses, possibly venting white steam.
