I believe it is a rifle length gas tube with a low profile gas block. I bought the one that was recommended when I was looking at the barrel. This is the first rifle style ar I built. Not sure about the short stroke. I do know I bought some rem 6.8 bullets so I can try it and keep the brass it did not cycling very well. switched to seller worked great then tried some hand loads from a friend and again functioned great. I am thinking that the rem bullets are the problem