Don't let the pistils confuse you. Their turning brown has only a little bit to do with the ripeness of your product... it is the trichomes that matter. When you still see a lot of white pistils, the plant is still in full bloom mode, still trying to gather pollen. I suspect that most all of your autos will finish around the same time and this one still has quite a ways to go before it is done. Use a loupe or a good magnifying glass and look closely at your trichomes, all over the plant. You will most likely find a few amber ones down low on the plant, on the fan leaves, but they don't count. The recommended advice is to wait for amber trichomes to show up at the very top of the plant, on the calyxes, and not on the sun leaves, and then the percentage level of how many of them are clear, cloudy or amber will determine the ripeness of the buds. Some people prefer pulling at 2% amber at the very top, and others prefer the plant to really be ripe, at 20% amber or more.
Whatever your preference, by the time it gets to showing amber trichomes at the very top, most varieties will have pulled back and changed to color, all of the white pistils. Furthermore, none of the white pistils will be sticking straight out as many of yours are. When you enter the last two weeks of the grow, where the buds will swell up sometimes to twice their present girth and weight, all of the pistils will be kinked at the top... none will be straight out... and during that last two weeks they will almost always, all turn colors.
Here is a hint that I give out a lot.... find a picture from the breeder of what your buds should look like at the finish. Compare that to your buds. That evidence alone should assure you that you still have a ways to go.