Try it .2 above and .2 below and see what you get. It generally is really close. But it depends on the powder. Varget and H4350 can have big swings. I've gained 120 fps with the same powder charge of H4350 in my 260 Rem with H4350. It was so much hotter that I was getting pressure signs with my normal load.
Like Chad said most of the time they are real close and sometimes spot on. I also go .2 step increments but will do .4 and .2 below in addition to the normal load. Measure velocity and adjust accordingly from there. That is if I am near the upper end of the load data.
If I had chosen a load more than one grain below max listed load I just load a few of my normal load and test for group and velocity and adjust from there.
Most of the time if the new powder yields within the extreme spread on velocity of the previous load then accuracy will be very similar. I also do not run out of ammo (good practice if running low on powder to save a few back) so can test normal load combination against new loads so comparing apples to apples.
That is what the guy that a teenager to reload did and I have seen no reason to change, has worked for me for over 35 years.