155' effective range? Indeed, overkill. That's with 20 pumps though... how many pumps do you estimate to get more practical/typical blaster ranges? (Between 100' and 70'.)
I dislike air guns for the necessity of pumping, lowering their RoF. I'd like to see just how far you could optimize the required pumping with this and find a nice balance of good RoF and reasonable range.
First of all, my vote goes for number five as well. Secondly, another thing to consider is using the contour drawings of blasters you find in their instruction manuals as templates for this sort of thing. So far I've just traced silhouettes of some photos of blasters for templates I've used in planning out paint jobs and sketches.