I use Universal Clays for skeet loads in both the 20 ga. and the 28 ga.

I have never had a problem with the powder bridging in the 20 ga. loader, but in the 28 ga., since the drop tube is a little smaller in diameter, it sometimes happens.

I load on MEC Grabbers, progressive loaders, so there is a powder charged dumped with each stroke of the handle, so I have developed the habit of giving the handle a little extra bump when it reaches the top of the stroke just to dislodge any bridged powder in the tube.

Universal is somewhat bulky and fluffy, so it is bad that way.

Do not rule out a double charge, or something on that order, like a 1/2 charge in one cartridge followed be 1-1/2 charge in the next one.