There was a post here somewhere. The guy posting had cut away the outside to show you what was inside. Keep looking, it is here! I can't seem to find it, someone else may know.
I removed the catalytic converter from the original exhaust CBR250RD model 2013.
Answer: Four chambers. A, B, C, & D:Well, I tried googling to find out the inner diagram of the stock exhaust, but found none. How many chambers it has to make that muffler almost silent.