Originally Posted By: Terry Lubzinski
Just to clarify or perhaps complicate the discussion, my understanding has been that the 12/C proof mark includes chamber lengths up to and including 2 3/4" and the 12/LC (long chamber) is reserved for 3" and over.

I concur: 12/C may be 2 1/2" or 2 3/4"; 12/LC is for chambers no less than 3".
RG