Being laid up for a week allows one to read too much. That and a new hobby in PPB's. Here is something I've noticed about what goes under the bullet, a wad stack.
Some like lube cookies, some like cork wads, some like felt, and some like ldpe wads. I am going to stick with target bore diameter loads here as I have no interest in hunting with these rifles.
What seems to be a pattern is most use some sort of material that provides either a shock absorber or provides a seal to the hot gas that keeps any flame cutting or leading from happening. Some have suggested that if it is a shock absorber, it would help prevent nose slumping.
I've seen more than a few top PPB experts write something such as I won't use a lube cookie, I'll only use a cork/felt/ldpe was. Or vice versa.
To a greater degree, aren't they all accomplishing a similar role. I also understand they are taking up space so a bullet can be seated out further. I understand a lube cookie in hunting loads where you'll "shoot dirty", but again, I'm only referring to target loads.