I'm just curious as to how much,if any, carbon build-up is normal at your gas block. I never really noticed it until i painted my barrel and now there's a nice black carbon streak and build-up at the gas block. I did put a bcm middy barrel and troy gas block on my m4 recently, but I haven't had any problems with it. I'm just curious.

According to most sources the carbon buildup is self limiting.  IE. when enough carbon builds up it flakes off.

I don't like a bunch of black shit on my bolt so I scrub it off.

Recently I have had luck soaking the carbon in CLP for 20 minutes then scraping it off with an abused 30cal brass brush.  Scrubbing at right angles to the long axis of the bolt while slowly rotating the bolt.

ETA. When soaking the carbon I place the bolt face down on a table and float a bead of CLP on the back of the bolt.  No need to waste a jar of CLP.

Also, don't forget to clean the inside of the bolt carrier, it usually has a bunch of carbon as well.

so the build up on the barrel will eventually stop when it gets clogged is what you are saying

More or less.
How much leakage you get depends on how well fitting the gas block is on the barrel.
If it's loose you get a lot of leakage.

Eventually, the hard carbon will plug the gap and you can then clean the external areas off and won't see much if any more outside.

Cool i was thinkin it was something like that. Much appreciated.

Good info for the bolt, but he was inquiring about the gas block.