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Well, here is some cold hard fact that decided the bulkiness of the rear. There is a AR15 lower used there. The widest cross section of an AR15 lower is about 1.4 inches. I have to leave some room for trigger links to pass those places, plus the outer skin thickness. The current width of the lower body is 1.78 inches, with about 0.09 inches each for the skin thickness. That translates to about .1 inches on each side for the link to pass through. If it is a clean sheet lower receiver design, I can easily trim off .2 inches for the thickness of the lower. However, if an AR15 receiver is used, there is very little room for trimming.

Before I lay up the fiber glass, the thumb hole looks big and Ergo feeling of the handling is also great. However, after adding the fiber glass thickness, the hole looks much smaller and ergo becomes sucky. Later on if I can make the lower with injection molding plastic,  I should be able to use pistol grip.

Some people also pointed out that the front hand guard is also bulky. Well, it is the same width with the lower. Theoretically the front end can be trimmed down but it nevertheless needs a step to connect to the rear. That would make the extrude aluminum upper less likely, hence higher manufacturing cost and the final price. The hand guard however, can loss the two side rail while maintain add-on rail option. That way, the front end bulkiness can be alleviated a little bit.

The adjustable stock would not make the existing stock any bulkier. If you go back to see my CAD picture of the lower, there is still a "buffer tube", only much shorter. I can implement a "collapsible" stock just like regular AR15's, only the locking mechanism need to be changed and adjustable range will be limited. However, the place after the AR lower receiver, since there is no pistol grip to be installed there, I have plenty of room to take care of that.