David,
you are right with "right" - as Jacob sayed AND Doc Ashby said also! I am quite sure it was written just so in one of his latest reports - available here on TradGang.
You can really observe the spinning effect Ashby is talking about! When you take a close look on your practise heads - after using them for some time - the color will first come off in spots along the left edge of the blade! See pic:
The encircled area has almost lost its color whereas the rest is still quite good. This abrasion effect here is caused due to the spinning action alone - indicating more pressure running along the left edge in comparison with the right side. The full ferrule is effected also - of course. Showing what resistance to penetration is caused here.
You can observe this "edge-effect" more or less on every Grizzly - depending little bit on what target material you use. If you want to speed up the process shoot them into a sandbar.
Cheers, Falk