Kdog
your Thomas image link does not work
That's strange I can see it
Jimmy is right on about the balance. You can get an 18” barrel gun to balance like the 15” if mill away some stock material in the front of the gun. Some guys go that way to get a little higher shot count. The 15” barrel will get about 75-80 shots at 20 fpe...and 150 or so at 12fpe. An 18” gun will get another 25% more.
Mike