Problem with a powder cop is you have to keep your eye on it. I use the RCBS lockout die. Works without monitoring. The RCBS is not precise. With the powders I use it's range is about 3gr. If I'm loading 5gr, I can set it to stop the press at, for example, a low of about 3.5 and high of 6.5, depending on caliber and powder used. Since my power measure has yet to vary, and I'm only worried about squibs and severe overloads, it works fine for me. When the powder drop is out of the range, the press comes to an abrupt halt whether you're watching the die or not.