AVIVIII got it right. A powder that is satisfactory with 3.5 grains will most likely not be safe at 5.9 grains. An inexact rule of thumb is that the pressure will increase as the square of the change in powder quantity if the loads are uncompressed. More if they are compressed. 5.9 is about 1.7 times more powder. 1.7²=2.9, so you are looking at almost three times more pressure, regardless of what powder and bullet are used.
In QuickLOAD, for example, a Speer 115 grain round nose FMJ at 1.69" COL over 3.5 grains of Bullseye produces a very safe 14,700 psi, while 5.9 grains produces 42,100 psi which just exceeds the +P+ SAAMI limit.
If I increase the bullet to Hornady's 124 grain FMJ, also seated to 1.69" COL, the predicted pressures are 19,800 psi and 61,500 psi. The first is safe, but the second will blow the case and damage the gun and maybe the shooter. The second is significantly compressed.
If I go still further to a 147 grain Hornady FMJ at 1.69" COL, the two pressures are 27,000 psi and 91,000 psi for 3.5 and 5.9 grains of Bullseye, respectively, thought the second load is so highly compressed (138% case capacity) that I doubt is could be assembled. The first pressure is getting near a maximum load, while the second will definitely destroy the gun and likely part of the shooter, as well.
We've already had one lost hand reported on the board recently, and don't need another. Pull the bullets.