I have two stainless rods for range rods and cleaning purposes. These have muzzle protectors made from ctg. brass & are held captive on the rod, by the jag.
I use a plastic coated spring-steel cleaning rod often for the .36 rifle's cleaning and range loading, although this rifle is very easily loaded with it's hickory
rod, even with .360" balls and .020" to .022" patches. Small calibers are easiest to load tightly as there is very little lead to move to conform to the bore.
Fiberglass rods, if not coated with something will rapidly wear the muzzle's crown. Use of a bore guide is quite necessary. They are like loading with a rat-
tailed file.
I did a test some years back and posted the results here. I cannot find it nor the photo now, however I will repeat what the basic results were. In the test, I
took a piece of octagonal barrel and clamped it in the vice. I rubbed one flat's corner with a variety of different materials, making 40 strokes with each. I tested
uncoated fiberglass, stainless steel, drill-rod tool steel, hickory, ramin, nylon, brass and aluminum.
The fiberglass cut a groove easily felt and seen, even in the picture I made of the test with a "new technology digital camera"if I remember correctly, the groove was over .025"
and looked like rifling groove in my Don Getz barrel, the stainless cut barely .003" deep, IIRC, the tool steel cut .001" and the brass, aluminum, hickory barely rubbed off the
blueing (TC). The brass rod cut ,001" same as the tool steel.
So - if using a hard rod, use a muzzle protector.
I recall reading that the military had "noted" some rifling damage from the issued steel rods in their muskets, rifled muskets and rifle muskets. The comments did not note wear, but
battering of the lands at the muzzle, most likely due to the loading orders of "Throwing" the rod onto the "ball" 3 times to ensure it's being seated on the powder.
I do see quite a number of people doing this at the rendezvous, but I have never seen any of them in the winner's circle, aside from the odd women when there were only 1 to 3 of
them shooting that contest.