[Unclenick]

I think this started with concern about cleaning from the muzzle with steel military rods. If you've looked at surplus military guns, a lot of old ones have funneled muzzles with no rifling left. That's due to the steel rods and also due to the soldiers being given more practice cleaning than shooting in many instances. Military barrels aren't disqualified for accuracy as early as a civilian shooter would consider one shot out, either.

Most of the modern concern with the soft metal rods is about embedded grit being in their surfaces. Steel rods are often made with coatings that can embed, too, but that's a red herring to me. The bore guide causes these rods to go in straight enough that they don't lean against one side of the bore or the other as they enter. That's what causes the funneling in the military muzzles to be as asymmetric as it usually is.

I use the bore guides for a couple of reasons. One is that I don't like getting cleaning compounds dripping down into the action from the chamber. That can spoil inletting by swelling wood unevenly or can affect glass bedding by lubricating it when it should be dry.

Another reason is I often put pretty sharp crowns on my guns. They do indeed shave coatings off rods and will cut the center out of a patch I try to push one into them when new, so I am having to clean them from the breech anyway. I suppose I could clean these rifles muzzle-down to protect the action from the cleaning compounds, but the guides are just easier, especially the Sinclair guides with the solvent port plug-in accessory, letting me put the gun in a cleaning vice or set it on bags without dribbling solvent all over it.

The final reason is that I still use a stainless rod and steel rods the coatings scraped off of before I had guides. Again, this prevents the rod leaning to one side or the other going into the bore.