Greg, I have the same scale from BPS and noticed a difference in my heads last season. They all grouped well so I didn't really worry about it.
I also noticed that my 3 Slick Tricks weighed 100, 100 and 101. My Razorsharks were all over the place between 97 and 103. But what is +/- 3 grains going to affect under 40 yards? I played around with components and my hunting arrows are all within 3 grains of one another. I can see where pro target shooters need more consistancy shooting out to 100 yards.