Curiosity aroused! I got out my homemade spine meter. It's worthless for getting actual AMO deflection but good for comparing one arrow to another.

My solid glass fishing arrow has .255" deflection. Compared to a 2315 that shows .295 deflection (I think Easton lists AMO deflection for 2315's at .340", so my weight is obviously a little light). A GoldTip 7595 checks .305". Anyway, that glass arrow is pretty darn stiff! It's not going to tune like a normal arrow.

Besides, it's drag from the line peeling off the reel that stabilizes the arrow. Without the line tied to the arrow, any tuning you do will be fruitless.