Touchhole reinforcement

[Ed]

This is the small barrel that I recently obtained.

I noted that the touchhole seems to be reinforced with some sort of insert. It is difficult to tell but I think that this "insert" (if it is) is non-magnetic.

As we have seen with other barrels, the corrosive nature of gunpowder can, and often did, erode the touchhole. Thing is that I have not noticed any sort of reinforcement on other barrels.

Thoughts?