One reason the starting and maximum loads are so close together is:
- you need a hot enough load with the older rifles to seal the chamber and get good pressure and burning.
- the max loads are conservative, being for older military rifles.
I shoot an 1894 Mauser Sporting Rifle in 6.5x55mm and a Ruger M77 MkII.
37.5 gr IMR 4064 with a Sierra or Speer 120-gr flat base shoots well in both of them.
I just happened to be loading some 8x60S with 4064, and decided to try it in some 6.5x55 which was up next, and it works. I have not tried to refine it further. IMR-4350 works so well with the lighter bullets, and 4350, 4831 and RL 22 with the 140s and 142s.
There are so many hunters here in SD who shoot modern 6.5x55 SWE bolt actions that I am sure there are plenty who have proven loads in almost any rifle, bullet and powder.