Sorry, just repeating information I've heard. Here is my source:
From "why single bevel broadheads" by Ed ashby
During the last 25 years I've intensely studied broadhead
design, and how it affects a hunting arrow's terminal
performance in tissues; field testing hundreds of different
heads in real tissues, dissecting wound channels and looking at
results. It's taken me that long to fully comprehend the 'how
and why' of single-bevel broadhead performance, and the numerous
and remarkable advantages it offers the bowhunter. The most
obvious functional difference between single and double-beveled
broadheads is the rotation single-bevels induce as the broadhead
penetrates.
Everyone knows that arrows rotate in flight, because of the
effect of the fletching. Few, however, give arrow rotation any
thought beyond that. And why should they? When using a double-
beveled broadhead all arrow rotation stops at impact and, unless
the broadhead is deviated in some way by impact with a hard
tissue, such as bone, the arrow penetrates straight through an
animal without any rotation. Examination of entrance and exit
wounds, and the intervening wound channel, confirms this.
During flight the typical arrow makes one complete
revolution (360 degrees) in about 60 inches of travel. Several
times I've measured the rotational rate exhibited for one
specific single-bevel broadhead design; the Modified Grizzly.
It's the broadhead I use for most of my hunting. Its single-
bevel edges induce one complete revolution in just under 16" of
soft-tissue travel (through 'pure meat'). / end quote
As I pull my single bevel heads out of foam targets I can feel them rotate as I pull them out.
With slower self bows it probably doesn't make a huge difference during flight to mismatch your bevels and fletchings, I agree with that. But that doesn't change the fact that a single bevel wants to rotate a certain way when it enters an animal.
