So here goes...........hopefully I do this right for yall. So just did my first 308. Ive milled and built 10 or so 556 lowers, and complete upper builds a couple times. Ive both pinned on complete uppers and full assemble some. But mil-spec being what it is.......these were easy peasy,cut and dry by comparison to a 308.......I knew this going into it and i'm fine with the learning curve. So specs on lower: Originally used a 3.8oz buffer that was sold as what to use for a 308. No idea on spring rate, as it was a set with the buffer, so at this point im assuming its wrong since now reading here 3.8oz is WRONG. Ive replaced that buffer with one from KAK @ 2.5" length and 5.1oz on my digital scale. Ordered a springco orange spring last night, so I know whats actually in there for the future, and Ive seen it mentioned here a good bit. The extension is the 7" internal dimension. The upper is a rear charging 16" mid-length heavy barrel from Bear Creek Arsenal. I did last night after a few weeks of lurking this site come across the "gas tubes,barrel gas port" thread, and that led me to check the location of where my gas tube ends inside the upper. It does NOT meet in the middle of the cam recess/cutout, and stops quite short by appx 3/16"(visual) from center. Therefore after some more reading and measuring what I have, it appears BCA used a DPMS mid-length tube @ 11.75", but it should have a Armalite spec'd 308 carbine tube @ 12.0625" and that will bring it up to center. This is going by the charts some of yall posted up here, so if I missed something, correct me please.