I think that it mostly depends on the powder being used since there's not much room for the cup to deform inside the tight bore.
And some powders like American Pioneer do require a lot of compression to get good velocity and accuracy.
There's so many variables.
But maybe that's why powder pellets can sometimes be more accurate than shooting loose powder, because the powder compression is performed by machines in advance and not when seating the bullet with the ramrod.
Last edited by arcticap; February 15, 2012 at 02:13 PM.