I have a question on barrel length. Right now I have a 375 H&H that I am using and it has a 24inch barrel. Now I am also having one built that is going to have a 28inch barrel. My question is should I be able to get 200fps faster than the 24inch barrel with the 28inch pipe using the same loads? Someone told me that you can expect to gain 40 to 65 fps per inch you add to a barrel. Is that a good guess or not?