The 4 or 5th pic from the bottom shows a big rip from start of rib down through the opposite chamber end
I think what you're refering to is the junction between the two breech plugs. This is not an integrity issue, it's just a poor fit resulting in a cosmetic issue. Nothup87, should you choose to abandone the reconstruction of this piece, PLEASE do not give (or sell) the barrels to anyone wishing to butcher them for any reason. I would be willing to buy them to build a flintlock should it come to that.
Cody