OK complete newbie offering an idea....

since I didnt know much about cleaning the breech plug bore - I went to what I did know. Since I have been around cars, motors my entire life, when we rebuild snowmobile carbs the jets really get tarnished up. Easiest thing to use is copper wire, strip some wire and run it down there and great a little friction.

Thats what I did, no way would the copper wire damage the breech plug and it really cleaned it up. HOwever plug has to come out of course for this, so it may be an extra step to some.....