Reloads or factory loads. Sometimes the rims on reloads can get flattened enough that they get oversized and will hang up. A MEC supersizer will bring them back to proper size. The reason I suggest this is that you are having the same problem with two different shotguns. When I was loading for my X's trap and skeet pumpguns this would pop up on occasion.

After the first shot the rest are just noise.