As said some photos would sure help. Some specs on the gun or at least the barrel would too.
Note: That lock is a JB special order edition of a left hand L&R English Queen Anne. It has a strange resemblance to a LH Siler. Honestly I was just happy to get anything.
It's been a good gun though.
My JB is one of his Carolinas with a 42" Straight octagonal to tapered round. I'm not sure if mine has a DoM Barrel or not. I know at times he used straight Colerain barrels and modified them. Mine looks like it may be a factory straight octagonal with the ring and tapered portion done by him.
There is no doubt his all round barrels are DOM as the whole barrel on his round barrel guns look "very homemade". As said the round portion of mine also looks "very homemade" but the octagonal portion looks professional.
What bore size is yours?
Is yours octagonal to round?
What loads do you shoot?
Before you throw the baby out with the bathwater, could the line be a layout pencil line or scribe line that did not take finish for some reason?
I do not agree with the concept of proofing a gun I'm going to use. Mainly because I do not have X ray vision and even if I did I do not know if I could recognize potential failure. To me it only proves it did not give way on the proof load and may set up failure for a milder load on down the road IMHO.
We all have our comfort level but I would feel more comfortable with a remote fired
long string gun in a tire shooter in a safe place realistic maximum test load instead of a crazy super duper proof.
I might consider removing the barrel and pulling the breech. I would check breech plug fit and makes sure the plug engages the inside face correctly. Look for fouling or gas leakage into the threads. This is a pretty basic but tedious skill any good gunmaker should master.
Honestly I should pull and inspect mine for obvious reasons so eloquently danced around in this thread.
If you do not like what you see, do not have faith in it regardless of what you see, or feel you have no business playing gun builder, contact someone like Bobby Hoyt and have him inspect or even possibly line the barrel before you scrap the gun.
If Bobby won't touch it with a ten foot pole, please pass that info along as he is an expert in his craft.