[mcguyver]

Our projectiles are very sub-sonic, and not usually prone to material failure during discharge or flight, unless you use cheap crap BBs.

The BB is lightweight enough and slow enough that gravity and air resistance affect it's trajectory more that anything else. That's why backspin is employed, to help overcome gravity and allow extra energy to overcome it as much as possible. Then, a polished BB will do as much as possible to cut through the air smoothly. Dimpling like a golf ball may help, but good luck making them in the billions needed, with good QC and still be as cheap as we pay now.

I think a rifled barrel for an AEG is a non-starter. The BBs themselves have too much dimensional variance to make that effective, and you'll either have under-spec BBs with no induced spin or over-spec causing a jam.