Thoughts on your tight bore...
When working up loads for cast bullets in centerfire rifles and handguns, I understand that leading in the barrel with moderate loads often is the result of the bullet lube. Leading towards the breach is from inadequate type lube and sometimes leading near the muzzle is caused by too little lube used.
Relating to your TC Hawken, if the PO was shooting conicals that were not lubed properly, he may have built up some leading near the muzzle, say the last 6 inches or so. After shooting PRB's the lead build-up may have been smoothed out so it is not readily visible.
You might try what I use for cleaning lead build-up out of handgun bores. Get some copper "Chore-Boy" brand scrub pads, (make sure they are copper, and not plated steel), wrap some of the strands around a tight bore brush and scrub the tight portion of the barrel. The copper is soft enough not to damage the steel bore, but will scrape out the lead. If that is the problem, you will see flakes of lead come out on the brush. Just a brush alone will not do it.
