I have a chrome lined barrel/chamber.  I can get the whole M4 clean as a whistle but notice a slight amount of carbon build up where the chamber neck meets the bore.  Just a small amount that is noticeable when peering through the bore after cleaning for inspection.  Does anyone else notice this and how do you get at it?  I use an Otis kit that works great but after 3 to 4 brush passes that slim ring of crap is still there.  What do you think, more passes? More cleaner?  I am just not sure it'll do it and obviously the chamber brush won't reach it.  Unless I am not driving it in far enough.  Thanks in advance!-Horik

If you've cleaned the bore and chamber properly, I honestly wouldn't worry about it.

How are you viewing this, a bore scope?

Naaa!  Just peering through with the ambient light coming from the other end.  Or the Otis fiber optic thing.  I feel stupid now though.  After looking through from the reciever end through the chamber I realized it was just the rifling grooves that were raised there.    From the other end I was sure it was build up.  Whoops!  I wrote this post before really thinking about it and I thought MAN!!!!!  it's wierd the rest of the rifle is spotless and this one spot is a bitch.  I usually detail the rifle after every 2 or 3 outings.  So thanks for the reply and all is now well.......:)