He's telling you the truth - every rifle has it's own personality and a variation of 10 grains of powder can make a big change in accuracy. If your rifle is getting accuracy that is acceptable to you, then there is no need to experiment, but if you are looking fo better accuacy you might want to test a few different powder charge weights. For hunting I usually start around 80 grains, then increase in 10 grain increments until accuracy drops off, thenback up to the highest accurate load I testedand use it for hunting.
Do NOT exceed the manufacturer's maximum recommended load!!!!!!!!!!!!