humdinger,
I'm most likely telling you something you already know, but make sure the barrel gets a good scrubbing every so often.
New user question...
Do these lead or copper build up super fast?
Ive put about 15-20 down the brand new barrel and need to clean it before my next range session.
Plastic fouling is oftentimes as big of an issue as the lead/copper residue.
Once you find a slug that you like and you've become acquainted with how it shoots, it'll be readily apparent when it's time for a good scrub.
20ish rounds always seemed like the magic number for me.