I've been using wooden rods, stainless rods and tool-steel rods for many years without bore protectors & without hurting the accuracy of my barrels. At this time, my .69 is perhaps the rifle most shot, since 1986 and it's accuracy is unchanged - indeed, it is shooting identical groups today with my poorer eyes than it was back in the late 80's. Perhaps accuracy has even improved probably due to the better powder today.
I had a brief excursion with a 7/16" diameter fiberglass rod - brown in colour, back in about 1975. I thoguht the larger size would reduce crown abrasion - not much, if any. I started with a 38" barrel and cut 1/4" off and recrowned it every 200 shots for a year. At 30" or 32", I retired it. That was the soft steel Bauska .50 with the 38" twist that I shot short slugs from. It's accuracy maintained 1" to 1 1/2" for about 100 to 150 shots, then the accuracy would gradually degrade to 2" around 200 shots, with no groups under 1 1/2". When that happened I'd cut off 1/4" and re-crown it.
I once showed a guy just how abrasive the rod was, by filing a groove on the corner of one flat with 10 strokes as if it was a file.