Swabbing with Rusty Duck might have been your problem. When I use anything other then pure 91% isopropyl alcohol for swabbing my sidelocks I often get hangfire or misfires. But in your case it was the cap that was causing the malfunction. So maybe it just needs to be broken in is all.

Good luck with your shooting and I will be looking forward to your reports.

And your right, shooting them is a lot of fun.