I think my main problem with this idea of chipping damage of the throat lands by the jag or rod end is that they do not come into direct contact on the way in. Or I should say I have never managed to make them contact on the way in.The issue with non use of bore guide is two fold alan
Damage cause to the throat and “area at end of chamber” cause by misaligned entry of jag / brush and rod - causes damage when the rod catches this critical area
One can see this as damage or chipping through a bore scope
Similar issues are seen at the crown with damaged edges but the cause of this is less likely to be cause by injudicious entry of a cleaning rod
Secondly I specifically said damage is caused when a bronze (or similar) brush changes direction within the confines of the barrel
The change in direction leaves microscopic imprint on the lands and grooves causing over time pitting
On a clean barrel scratches / pitting are easily seen with a borescope
Use of a guide prevents the damage to the throat area aided by the rod
Use of nylon or similar brushes prevents damage to the bore when changing direction within it when solvent is “scrubbed” especially if those bronze bristles have particles of carbon attached to them , which will assist in damaging the internal finish of the bore
Use or don’t use a bore guide your choice , your barrel
They’re expendable items anyway
The cloth patch itself is the insulator / centraliser which is the only part that is in contact, whether a guide is used or not. The bristles of the brush also are the only bit in contact...the tip and spine are centralised by the bristles.
The only time my aluminium jag is in contact with the lands is when it is trailing out on withdrawal when the patch has come off, and that occurs even when I am using a bore guide.
The particles of carbon that are picked up and scraped against the bore by either the patch or the nylon/bronze brush bristles are only from the last shot. The previous bullet picked up and scored the majority of the residue down the barrel under 50,000psi more pressure than the patch or bristles do.
It is this huge order of difference in pressure of rubbing abrasive down the bore that I find difficult to ignore.
The burnishing of the lands by the side of the rod is also minimal in comparison... I use both steel and Agate burnishers for finishing and setting stones and know just how hard you need to press even with a soft metal like silver to make any impression.
I know that soft materials can and do pick up and carry abrasives, but I also know that even with saturated abrasives or things like emery cloth, the more pressure behind them the more effective they are. The relatively soft metal of the bullet does this under huge pressure with every shot fired.
I am intrigued by your description of the point loading of the bronze bristles on reversing the direction in the bore. I will need to think about that a bit more...concentrating pressure like fullers when forging or dimples from stilleto heels come to mind!
I use a nylon brush and an aluminium jag in order not to get false copper dissolve readings from the patches, rather than for any bore damage limitation reasons.
To be clear for the OP I invariably use a bore guide when using a cleaning rod with patches, brush and chemicals...I find them convenient for a number of reasons...but the prevention of excessive wear is not one of them.