I know that you're asking about the front of the rifle, which appears to be an upside down stormie E-11. Most builds that I have seen of this actually cut in the ridges into the pipe, as opposed to gluing on t-track. I was going to buy cheap wiper blades and use the wiper edge as t-track if i needed to.
After doing a quick google search, it looks like an even split between t-track and grooves, judging by people's builds, plans, screenshots, etc. I know that Woodchuck does his barrels as cut-in trenches the same way I did mine, and he's the most respected prop gun builder on the clone troopers forum, IMHO.