I asked this question once before and got confused again. I have this 18 1/2 ", cut-down WIN barrel with two grooves in .308. How was this done? Is it a chamber sleeve, or is it a sleeve the entire length of the barrel? I know they never made a .308 barrel, or a two groove barrel. I read a chamber insert can be removed with a broken case extractor. Any truth to that? Worst part is a WIN unmodified op rod came with the barrel, shortened to go with it.