Torque vs stretch is a subject that's always interested me. I Drag raced for 20+ years, did my own engine work, got into buying aftermarket connecting rod bolts. ARP was the supplier - they had several tech articles (which I found quite interesting) on their web site. (going from memory here) One article suggested that measuring stretch of the bolt was a superior method for installing rod bolts. Explained that torque to turn a fastener is affected by surface finish of the threads plus any shoulders, fit of male to female threads and lubrication. They sold a rod bolt stretch gauge that included a dial indicator to measure the stretch in thousandths. My particular application used a 7/16" fine thread fastener, their instructions recommended a stretch of .005 ~ .006". claimed that a fastener is strongest at its elastic limit (if you go past, it won't return to its original length, and you should replace it). It takes ~ 95 ft lbs to stretch a high tensile 7/16" rod bolt .0055". They also recognized that not everyone would use a stretch gauge and included a chart of recommended torque values based on lubrication. Highest recommended torque values were for bolts lubed with 30 wt engine oil, lowest were for those lubed with their "moly lube" (assumed equal stretch). They also recommended that a fastener be brought up to torque or stretch at least 3 times because there is always a certain amount of burnishing of the (new) threads together, especially on the first 2 or 3 times.
Sorry for rambling.
So, yes indeed, threads on a barrel will stretch the end of the barrel, especially @ 100 ft lbs or more but hard to measure until you get to the higher values.
But I'm with those suggesting much lower torque values, I install mine just "snug" - probably not more than 35 ft. lbs. Never had one come loose. If you think about it, a right-hand twist barrel would tend to tighten itself if anything.
