FYI...I agree that QLA's are a PITA for using nothing but patched round balls and I no longer own any TC barrels with QLA.
However, on the subject of 1:66" vs. 1:48"....I personally ran side x side tests with my TC 1:66" and TC 1:48" barrels last summer...I ran these tests in sets of .45cal, .50cal, and .54cal barrels...one set of caliber barrels on each of three different Saturdays at my range, with everything else being precisely the same at the time of the tests....equipment, procedures, products, weather, lighting, shooter, etc, etc
My hunting loads are:
90grns Goex 3F (3F)
Oxyoke wonder wads
.018" TC prelubed pillow ticking
Hornady .440/.490/.530 balls
If you shuffled the targets together and handed them back to me I'd have to pause and study them to try and figure out which ones were made with the 1:66 vs the 1:48.
IMO, assuming proper components in good condition barrels, the notion that a patched ball will skip rifling is an old wives tale...like the old wives tale that 1:48" twists won't shoot round balls accuratey.
I bought round ball barrels because I had heard the old wives tale about 1:48's...now I know better from first hand experience that I didn't need to.