I recently bought a used 870 Wingmaster. While I was cleaning the 870, I noticed alot of carbon build up inside the magazine cap and on the top side (muzzle end) of the magazine tube. I cleaned everything up on the receiver.

Then I started the barrel. I noticed it had 2 holes inside the retaining ring (not sure what its called) on the barrel that secures the barrel to the magazine tube. The buildup on carbon appears to be from these gas ports.

What is the purpose? Is this normal?