I have an old Shooting Chrony that I've had since new. I know it's not top of the line, but it has given me a general idea of velocities. Last time I had it out, the velocities didn't seem the change much, even when trying a different load. So my trust isn't there anymore. I'm going to borrow a magnetospeed and set up both for comparison, before I spend money on another. But I wonder just what could have gone bad to cause erratic readouts? This has never been shot, never out in the rain.
