In a deadline pinch I would download toolbag trial and get the project done that way. A fix for this situation can be a learning experience at a later hour.
you could solve that pinch by triangulating this part tho. but it would only work in this case, on curved surfaces you can usually not get away with this
Looks great. The design reminds me (slightly) of Human Revolution's machine pistol. What's with the pinching on the corners of the oblong inset for the stock to slide back into?