Actually RCBS advertises .1 grain accuracy for the 1500. The A&D FX-120i Lab Balance I use with my V3 Autotrickler is .02 grains, and the Sartorious GD 503 is accurate to .005.
There is an interesting article on accurate shooter. A contributor threw low, medium, and large charges with his 1500 and weighed them on his FX120i.
Summary:
"Looked at one way, this test is entirely unfair to the Chargemaster. RCBS has never claimed anything other than 0.1 grain precision for that scale. Holding it to an accuracy level of 0.04 grains seems a very high bar, indeed. And yet the Chargemaster hit that level on ten out of 27 throws.
I'd call that good."
Here is a link to the article: