Good Job.
its a little unclear what you changed exactly, but still nice job.
Notable Things.
1- You should probably place the various gun pieces into their own "movie-clips" which will then slide out, and slide in from the sides, much like other games similar to this one.
2- Add a color system that goes "By Part" along with #1, which will allow the user to change the color of each part individually, its not that hard really, just overlay a transparent color layer over all the weapons (to maintain the shadowing and detailing you've done so well) and connect the color layer's color and transparencies to a variable, which you can then connect to a control like a slider.
3- The layering system can get just a tad bit annoying, I would suggest adding a system (preferably something in the right click menu) that will move the selected part up or down 1 level in flashes built in layering system. This should make part conflicts much easier to deal with for both you and the user.
4- Perhaps later once you get more proficient with flash, I would suggest adding an Import/Export system in order to preserve the alpha that the weapons have in their images, while Prnt/Scrn works most of the time, it can be VERY finicky about alpha/transparent colors, like glass, and your lasers, which can make things difficult down the line.
5- Way down the line once your satisfied with the customization perhaps you can add a simple shooting gallery and connect stat variables to each part, it doesn't have to be anything to fancy, just a simple movieclip containing the pieced together gun in a 2d platformer perspective, and a small display of the weapons stats across the bottom of the screen.
Great resource for weapon idea's for sure. OH and one more thing
6- If you want, add sci-fi attachments, like a blob launcher barrel, or a steam-punk scrap launcher set, or maybe even a star-wars like laser gun assembly, And if your feeling particularly creative why not make the octopus and shark cannon from saints row *laughs* it'd be hilarious.
good luck with CAG4