What is bore frosting?

[Ignition Override]

If we can exclude lack of cleaning of corrosive primer residue, is it primarily from erosion or some oxidation?

With a basic $8 bore light, is it commonly used to describe any land's surface which does not have much shine?
I suppose that pitting is easier to spot, and appears more irregular with some depth?

 

[geo57]

IMO and my experiences with rifles over 45 years, frosting won't come from erosion or wear. As you already mentioned a lack of cleaning corrosive salts, the other main cause of frosting / light rusting is humidity issues mixed with poor storage practices ( leaving guns in cloth cases , putting them in there when cold and left in a warm house, lack of a bit of oil for preservation in problem moist areas such as basements, etc. )

To me, frosting is light rusting. If lands or groves have this, yes they won't be real shiny, but they may not be real shiny and have have no rust or frost. I'd imagine some shooters will agree with this take on it while others will have a different opinion and what it means to them.

While it does detract from the looks of a bore, some frost usually won't effect practcal accuracy a whole lot or any at all for most non competitive shooters. My very first MI Garand had a bore that was worse than many sewer pipes I used to replace when I plumbed for a living. No exageration. That darn thing would shoot 2" 100 yard groups all day from a prone position.

 

[BrocLuno]

To me, frosting describes a sightly dull silvery finish to the lands (and maybe the grooves). I believe it is the result of surface corrosion that got cleaned away (the brown part) and left behind the slightly uneven surface. It may have been shot away, or scrubbed away.

I've only had one old barrel that was "frosty". Since it was never going to be a keeper (I already had a replacement in hand), I went after it with a long dowel wrapped with crocus cloth and well oiled. Driven by a drill motor and up and down the bore for maybe 10 minutes.

Scrubbed it out and looked about every 3~4 minutes. I could not "sand" it away with that fine an abrasive. So I know the surface irregularities were at least a few thousands on an inch deep

When I started, it looked like a cold solder joint - flat and silver. When I was done experimenting, it looked slightly glossy, but still mostly flat and silvery with a common Browning bore light.

 

[Ignition Override]

Descriptions of many of the gun bores at "Joesalter" include the word frosting, but my interests there are WW2-early 50s production (Enfields).

I've seldom noticed the word used on GB, but many sellers there might be unfamiliar or lacking the equipment to evaluate bores.