The salt technique does work, though it is more typically seen on larger-scale models to simulate chipping paint.
The key is letting it dry properly during the application and then after the second coat of paint.
Look here for a good tutorial of how to accomplish it:
https://www.scalemodelguide.com/painting-weathering/weathering/apply-realistic-paint-chips-salt/To simulate a digicam look, it might be difficult only because of the planning you will perforce put into it. You have to imagine your scheme in reverse. That is perhaps the hardest part mentally. Physically, it will take a long time to do a single model.
Say you want a tricolor camo scheme. You would have to base coat the model, then coat the areas that will
not get the secondary and tertiary colors in the 'salt wash'. Then paint the second color. Then remove the areas you want to get the third color and selecgtively paint those.
Ultimately, I recommend the sponge technique, but an even easier method--especially with BattleMechs and their hard-to-reach areas and negative spaces--is to take an old brush and cut irregular swatches from it to use in lieu of the actual sponge. Then you are effectively stippling the model with your color scheme.
As
Worktroll and
Joel47 have ably pointed out, you are really looking for the
effect of digicam, not specifically the
application per se.
Not the best picture, but it gets the point across of the stippling technique: