I only loaded and shot 300 AA shells with PP. They were consistent.
My setup is a Grabber 761R from 1981 and a red PC powder baffle. No problems.
The only time I had powder bridging was with International in a 20 gauge Grabber with the same PC baffle.
I use the standard MEC grommet and brass washer with that loader and powder now. Fixed the problem.
That brass washer is a wear item. A fresh washer and only moderate torque on the powder bottle and ball powders run fine in MEC loaders.
I'm of the opinion that most squibs loaded on MEC equipment are not in fact from powder bridging but rather from migration of that brass washer - it slides back and forth instead of staying put and partially blocks the powder drop.
