Have you tested your powder/charge to see what a double looks like? This is one of the reasons I got started reloading using 124gr 9mm and Universal Clays. A double charge will overflow the case. Even with the smaller charges suitable for 147gr, a double of Universal will pretty much fill the case such that it'd be hard not to notice. I also agree with a previous poster, frequent interruptions (to weigh powder charges or for any other reason) are a great way to introduce human error and end up with a double charge or squib. The squibs I've had were, AFAIK, all due to stopping to deal with primer slide malfunctions, and screwing up when getting back to loading. Wanna kill these ads? We can help!