I saw your bull barrel front sight base and called customer service to get the correct size to turn my barrels to. The gentleman on the phone said they would fit .938 barrels, so I asked him what I.D. (inner diameter) the D.P.M.S. A2 Bull barrel FSB was. He said they were .938, I tried to explain to him that a .938 barrel will not fit into a .938 FSB, there must be some clearance, two parts cannot occupy the same space at the same time. This gentleman was very nice, and he tried his hardest, but he really could'nt help, he said he did not have any calipers or one of the front sight bases around to measure for me. My question is: should I turn my barrels to .936-.937 to fit into a .938 FSB, or, is your FSB actually .939-.940 to accomodate a .938 barrel. As one can see, if I machine my barrels to .936 and the fsb is .940...then I have a nice visible gap between the two parts. Part of the problem is how your discreption in the Catalog is worded. Can you please clarify for myself and others, as this topic has come up on other AR communities and nobody seems to have the answer. Thanks in advance for wonderful products and customer service.