I recently ordered two of the premium lower build kits. One of the triggers was silky smooth from the first pull, and the second was gritty as you describe. After a couple hundred trigger pulls, the gritty trigger has begun to smooth out considerably. I honestly don't know if anything can be done about it, as the imperfections that cause the gritty feeling are super small. Someone with the patience of an oak, a laser-leveled eye and a steady hand may be able to improve a gritty trigger with some Flitz and a Q-tip, but I wouldn't recommend it- just shoot it.