I have only used the multi metal "red" ones from BPI and the chilled shot they have in #6 along with their overshot cards and have nothing but awesome results. I am not or looking to experiment with a great gun setup I have.

http://www.ballisticproducts.com/prodinfo.asp?number=3221235US

http://www.ballisticproducts.com/prodinfo.asp?number=N712

It all depends on the powder, charges, primers, shot and too many other factors to pinpoint why one gun shoots wel and others do not even with the same load data. I use Pyrodex RS Loose and use 110 grains with the wads above and either #4 or #6 chilled lead shot with Remington Kleenbore 209 Primers and the overshot cards above. The packing tight works well for me and I do it all the time.

As far as the jug choke it is supposed to be larger than your choke on the end of the gun. What happens in theory is the shot moves its way up the bore and expands in that area and is constricted before exit by use of the choke on the end of the gun. This only works if you choose not to load the shot with a wad. If you use a wad then the shot is still inside the wad at this point. The wad and shot do not seperate until after outside the barrel. That is why I truly believe that packing it tight gives me those awesome results at long ranges because I can find my shot wads typically 40 yards or so from where I shot the gun which means the shot and wad do seperate somewhere in between and that speed is impressive it the wads are at the 40 yard range.