Just as an experiment try a tighter fitting bullet. Even if it's one you don't want to hunt with.
The Fed bullet will move the sleeve for a tighter fit when fired, but it has to fire first.
The Thor bullet is the same way. It expands when fired. I had some loose fitting Thor bullets that wouldn't fire off BH 209. The primer would fire, and just push out the bullet 10ft. Using a tighter fitting Thor worked fine.
Just to eliminate the bullet being a problem. Use something tighter, and do everything else the same except swabbing.