I do not have the J107 but I recently purchased the Phantom from a guy here on LRH. I was pleasantly surprised that my heavy tactical .308 fit nicely inside and I'm guessing that Eberlestock
uses the same scabbard for both packs. My .308 only has a 24" barrel but its in a McMillan A5, with a Mark4 mounted on a 20 moa rail. Its not a huge rifle but its definitely a lot bigger than the average hunting rifle with sporter contour and smaller glass.