That's surprising to hear...I shoot TC Hawkens, same barrels as Renegades, and patched round balls with Goex are outstanding...I use TC's .018" prelubed pillow ticking patches for tightest groups...unless you have some sort of strange manufacturing defect in your barrel, I'd think something else must be a work here...ie: sabots worked better and it may be that's because they're sealing tight for shot to shot consistency...what size ball and thickness of patch are you using?
I use Hornady .490's with 50-70grns Goex FFFg and the .018" prelubed pillow ticking patch.
For powerful 90grn Goex FFFg hunting loads, I add a prelubed oxyoke wonderwad over the powder as extra firewall/seal/lube.
But to your question, remember that TC barrels use patent breeches therefore, the pellets would stop and sit on top of the patent breech...a long way up and away from the nipple's fire channel, unlike loose powder that settles all the way down into the tapered cone of the patent breech...so I can't imagine that pellets would work well in a TC side lock percussion like a Renegade or Hawken
