I'm also building a form 1 pistol can. I went with a 7.6" B tube from SDTA thinking that the slimmer can would work better with sights. I'm still waiting for Chris at Diversified Machine to get me my Ti "shot glasses" to finish it and see how it works. I'm hoping that the B tube was the right choice since I plan to use it on 45 as well as 9. I'm interested to see what you decide.