Call TC. If they say shoot it, get the name/ext of the person you speaking to.

JB is great, do not run steel wool in your barrel, there is a reason cleaning brushes are made of phosphor bronze.

My guess is that it is some of the protectant that TC applies to the bore before shipping. With the rifle in a vise, a good scrubbing with a new brush will get you clean as a whistle.

The Otis system is handy, but, will not get you there.

YMMV