Cosmose: yes, you WILL get more punch. A lot more. These suckers are going almost an extra 100fps for every inch of barrel added, at least out to 4" (NAA's max is 4", the MiniMaster) where it does 1,400fps. Figure 1,500+ in a Single Six.
Now look at that pic again. The round is nowhere NEAR the "come unglued" point. That little booger is good for several hundred more FPS before significantly fragmenting.
At some point, the tougher original formula +V would be a better choice. Dunno where that point is though...somewhere between 6" and 9" would be my guess, from a 9" barrel Single Six that TNT might come apart. That's based on that pic, guesstimating how much more speed would make the "mushroom" come apart. But it's pure guess without test data.