Looks like I'm late to the party. I'm using a 20" T-box barrel, JP bolt, SLR adjustable gas block,using SIG M400 receiver set. I use the 123gr SST factory loads for hunting and reload that brass with 123gr SMK using 8208 xbr for target shooting. I haven't used it for any matches yet but planning to run it next year. Planning to build another with a 16" barrel in the future