Exceptional work on those alien dead remains suspended in tubes. This has a lot going on for it, im not sure if the bottom ribbed designs are bones or tubes or other weirdness but it looks great. Lots of visual interest, but perfectly clear in the playspace.
Your magazine tube is way too scrawny. The entire shotshell has to fit inside there, including the rim of the brass. The mag tube should be larger in diameter than the barrel. Also, the barrel flares at the chamber side, it isn't a step.
I have baked the tubes and brackets in a different meshes: Besides, I increased the antialias to 8x8 and the bolts look better now without modify the high poly model (just in the brackets, I need to do the same with the tubes).
Looking cool, would be fun to see more volume tho. I would suggest wrapping things more together with eachother, a tube going under other tubes, twisting together, jutting more up or down, etc.
there's also a seneca script that creates tubing on the path of the selected edges. Alongside beveling and deleting inward polys and making tubes out of remaining corner polys, I saw him using that 'makepipe'(or somthing else) script too.