There might be something else at play here if that is a White Lightning liner.
DO NOT INTERPRET THIS AS A DESPARAGING REMARK ABOUT JIM'S LINERS. I AM A LOYAL FAN.
I noticed on my last build that the thread on a White Lightning does not continue right to the countersink. It stops just a few thou short - leaving just a bit of a shoulder, which varies in width from liner to liner. That shoulder prevents the liner from fully seating in the countersink. The only remedies I came up with were to slightly counter-bore the thread in the barrel (which I would not do) or swage the edges of the liner into the countersink ( which I did). I even considered cutting the shoulder away on the lathe. Perhaps the OP has a similar situation.
I don't want to hijack this thread, but am curious to know if others have similar experiences and what their solutions were. This should probably be a separate thread if there is anything to discuss.