Every third or fourth clean of any of my rifles also includes an additional inspection of the crown. Since I use mods on all my calibers, carbon build-up on all the crowns is a given. Inevitably the crown gets wet on each inclement outing, so the chance of fostering a corrosive paste on the most important part of your barrel seems real enough to me.
Some folk declare crown carbon build-up does not happen on their rifles. Penny to a pound they are the same folk who call for reinforcements when looking for socks...
Cleaning the crown is likely to be a marmite thing. But let me submit this photo montage as evidence for its need and the method that works for me. The crown gets crusty so the first thing I do is push a dry patch to the mouth before wafting the crud off
. The best tool for removing the carbon that chemicals won't lift is a glass fibre pencil
and with accurate application the crud comes away
and can then be removed with a vacuum
to leave a much improved muzzle 
Some folk declare crown carbon build-up does not happen on their rifles. Penny to a pound they are the same folk who call for reinforcements when looking for socks...
Cleaning the crown is likely to be a marmite thing. But let me submit this photo montage as evidence for its need and the method that works for me. The crown gets crusty so the first thing I do is push a dry patch to the mouth before wafting the crud off
. The best tool for removing the carbon that chemicals won't lift is a glass fibre pencil
and with accurate application the crud comes away
and can then be removed with a vacuum
to leave a much improved muzzle 



