Hey Doc Drew,
It's possible that there are a bit more 'alternees' than you are thinking. For instance, in your first two pictures, the 2 iron and the Parker D3, it looks like the 'lopin' have better than 20 layers prior to twisting.
It's possible that both those barrels started with very similar 'lopin', I count somewhere around 24 layers for both. The difference is likely that the 'lopin' on the Parker D3 example was drawn down, forged, to a smaller square cross section before twisting. Just thoughts is all.
