If you read the article TL linked to, the author seems to have had the issue even in hunting rifles (though to be fair, these were Varmint rifles, which are often built pretty tightly).
I have to say, in all the years I've been shooting, and despite having routinely used a borescope ever since the Hawkeye came out, this carbon issue has never even been on my radar. The one bit of carbon I've had trouble removing has been what accumulated in the corner of the step in the chamber that corresponds to the cartridge case mouth profile and that limits neck length, and if you trim your brass, that doesn't present an interference issue.
The main pressure and accuracy thing I've had issues with in some production barrels is copper accumulation narrowing a bore forward of the throat (where the bullet is traveling as the pressure peaks, upsetting it radially to increase friction). A cleaning problem is that copper and powder fouling will lay down in alternating thin partially covering layers, so some copper dissolving chemistry will slow down trying to get through a carbon fouling layers if it doesn't have adequate detergency or carbon removal abilities of its own (Bore Tech Eliminator has both, which is part of why it works well). But I don't recall any barrel I'd cleared of excess copper still having any visible carbon left other than at the aforementioned location.
I found out by trial and error that wetting that carbonized chamber profile inside corner with Gunzilla and letting it sit overnight would loosen it for patching out cleanly. I'm sure Slip2000 Carbon Killer would soften it for brushing and patching out, too, and much faster. Indeed, I'd be tempted to double-gang a carbon ring by letting the Carbon Killer soften it for ten or fifteen minutes, patching it out, and then using Boretech C4 and patches for final carbon removal to see If I couldn't avoid the brushes altogether.
But before I went there, I'd have to see the problem first. Drat! Now I'm going to be doing some range scoping after every shot, looking for this issue to appear. Bother!
I have to say, in all the years I've been shooting, and despite having routinely used a borescope ever since the Hawkeye came out, this carbon issue has never even been on my radar. The one bit of carbon I've had trouble removing has been what accumulated in the corner of the step in the chamber that corresponds to the cartridge case mouth profile and that limits neck length, and if you trim your brass, that doesn't present an interference issue.
The main pressure and accuracy thing I've had issues with in some production barrels is copper accumulation narrowing a bore forward of the throat (where the bullet is traveling as the pressure peaks, upsetting it radially to increase friction). A cleaning problem is that copper and powder fouling will lay down in alternating thin partially covering layers, so some copper dissolving chemistry will slow down trying to get through a carbon fouling layers if it doesn't have adequate detergency or carbon removal abilities of its own (Bore Tech Eliminator has both, which is part of why it works well). But I don't recall any barrel I'd cleared of excess copper still having any visible carbon left other than at the aforementioned location.
I found out by trial and error that wetting that carbonized chamber profile inside corner with Gunzilla and letting it sit overnight would loosen it for patching out cleanly. I'm sure Slip2000 Carbon Killer would soften it for brushing and patching out, too, and much faster. Indeed, I'd be tempted to double-gang a carbon ring by letting the Carbon Killer soften it for ten or fifteen minutes, patching it out, and then using Boretech C4 and patches for final carbon removal to see If I couldn't avoid the brushes altogether.
But before I went there, I'd have to see the problem first. Drat! Now I'm going to be doing some range scoping after every shot, looking for this issue to appear. Bother!