I've been raising the handle also and moving the bar over slowly so the shot more or less trickles down the tube. While this slows down the time to reload a shell, it's working very well. No more bridging

It's America, Greg. Do as you like. Frank found that the cause of the bridging was the restriction at the end of the ram tube, corrected it and cured his problem. 9000, 600Jr, or Sizemaster, the ram tube design is the same, so I think it's reasonable to start there. I'll agree with you (yeah, rare, right?) that the tube ID on the .410 is smaller than the 28, though if it bridges with with 71/2, It's likely to bridge with#8.
My only point in my previous post was to bring attention to Frank's cure of the restriction.

Allen, I do the same as Bill. While raising the handle or tube, I tap the tube with a small rubber mallot. With the Mec Jr, it's a matter of feel and listening to the shot and powder dropping. No "magic pill" for this problem. I've never filed, altered or washed shot. It happens even with 20s and 28s, regardless of the shot size. I rely mostly on the sound of the drop, before I lift the tube completely out of the hull.