Test 2 - mind you, nothing scientific about these tests, however they were enlightening to me and I trust the results enough that I will not use stainless nor drill rod without a muzzle protector from now on.
Note that in each test, by 80 foreward strokes. I did not count the back stroke that was made each and every time. So - the actual stroke in the materials, was 40, 80 and 160.
This time, I used, left to right, brass, nylon, drill rod, stainless rod and wooden (hickory) wiping stick. The last three are of course, the fiberglass rod test. In this test, test 2, I made 80 full strokes (each way) with each material, identical to the final test with fiberglass @ 80 strokes - all materials were round and 3/8" or smaller in diameter except for the nylon rod, which was 1/2" diameter. That might have skewed the results, but I doubt it. The 'feel' of each material was telling and could almost predict the results. The fiberglass rod felt like a very find file and showed this by it's damage to the corner. The brss rod was not as long as the others, so the stroke was shortened by about 15% (est). There was enough difference in damage between the brass and the stainless steel though, that the brass wins as being less abrasive regardless of it's slightly shorter strokes.
The marks ont he barrel, in order of least damage:- wood, nylon, brass, drill rod, stainless, then the three grooves cut by the bare fiberglass rod. Note that the stainless at 80 strokes is almost equivalent to the fiberglass at 20. Seems to me, stainless steel (don't know what grade) was deemed to cause the most damage in the test done in Muzzle Blasts magazine- 1 or 2 years ago. The stainless I used was very hard - aircraft grade, whatever that is. A softer 416 stainless might not do as much damage, or maybe even more - I don't know. I do not know remember which gave the least damage in their test, but I do think my test is representative to the effects of each material. An electric powdered hacksaw would work well, I think, in a more controlled test, as there would be no rocking of the rod as even a stroke with the arm gives.
Note - I can not see (5X hoop) nor feel any damage from the wooden rod, even though the bluing is removed, ie: worn away by the friction of 80 strokes. All the other materials left divits I can not only see with the naked eye, but also feel with a fingernail, including the nylon rod, second-best in the test. That may be why there is a small divot in the muzzle of my .69 as that is it's cleaning rod and has been for the last 15 years. The first 10 years, I used a hickory rod. Guess I shouldn't have switched.
The muzzle of the .69 - look at 11 o'clock in the picture, is a small groove running up against the land. Holding the barrel exactly the same each time it's cleaned, will make the rod flex pretty much the same each time. Over time, this can cause a groove to be cut. I'm sure this is why that groove is there. Now, be assured it has not hurt the accuracy of this rifle - last year it shot a 6 shot group off the bags at 200 yards - 1 1/4" wide by 3 1/2" high. bore .690", ball .684", patch .030" (by calipers) powder charge 140gr. 2F GOEX shot 'dirty' no wiping while shooting - ever.
I am certain a smaller bore would not be as forgiving of minor muzzle damage, just as with modern guns. The smaller the bore, the more perfect everything has to be.
