Who says they're not the same diameter?[8D]

One of the things I like about Carbon Express Terminators is I can have the smaller diameter of a carbon arrow with the weight of a 2315. Nice to have when I'm trying to punch thru both sides of a 300-400 pound hog.

But even if one arrow is 5/16 diameter and the other is 23/64ths, the smaller diameter and lower drag coefficient would not offset the lower momentum. Not even using significantly less fletching on the light arrow will allow it to retain as much of it's energy as the heavier one will, even though it will retain more than it would otherwise. It's the lack of momentum that causes the lighter arrow to lose it's speed and energy at a faster rate than heavier ones.

In practical terms though, the speed and energy dropoff doesn't really get dramatic until after the arrow has gone 40 yards. As I mentioned earlier, when I tried 2213's on my old bow, my pin gaps between my 20, 30 and 40 pins were closer and there was a HUGE gap between the 40 and 50, and a wider gap between my 50 and 60 pins. With the 2216's, the pin gaps were a lot more consistant. There wasn't much more gap between the 40-50 and 50-60 than there was between the 30-40 pins.

Where the fallacy comes into play is trying to use exceedingly light arrows to flatten trajectories for hunting shots beyond 40 yards. The guys that are doing it, if you'll notice, are using broadheads that are usually reserved for light equipment; small, thin ferrules with cutting diameters of 1" or less.