More progress was made after sourcing a strain gauge from a handheld digital scale. This will allow to compensate for variations in elasticity due to temperature and the rubber hysteresis effect by measuring tension and factoring it into the ballistic calculation. Slots for it and the required linkage were cut, followed by some more work on the magazine well, stoppers, and the butt plate insert.

The aluminium parts for the projectile ramp were cut and ground to shape. A captive nut assembly was constructed out of aluminium pipe, then the rest of the main motor assembly. 

 And then I had a little accident where my Dremel saw blade slipped into my left middle finger, requiring a visit to the ER for some stitches. I wasn’t sure I would be able to include all the features I wanted before the deadline but now I guess I’ll just have to focus on getting it to any working condition with less time and without the full use of my limbs. Wish me luck!