This is going to end up being a game model. And near the buffer tube, There is a horizontal annotation line which I have added, I wanted to achieve that form change where there is "bulge" flowing all the way up to the cylinderical shape near the buffer tube. I'm not sure how I can achieve that without using some boolean…
The red tube and area around that needs a bit of work. The tube is a lot more outward in the concept, rounder too, and the helmet underneath looks a bit too flat, like a slanted roof instead of a curve.