Since I said I would NOT post anymore in the thread Skeeter Load in a M696 so as not to upset anyone I measured as near as I could and the rear of a barrel on a M69 is roughly .062 to .063 inches barrel wall thickness at the beginning of the forcing cone. A M629 is roughly .094 inches thick at the beginning of the forcing cone.
Keep in mind that is what I obtained and is most certainly challengeable by anyone with more skills than I as my skills are pretty inept.