In actual fact, the correct way to use a pattern plate is by tracking the gun across an arc and as you pass the aiming mark on the plate you fire. This is supposed to give a more realist interpretation of the shot pattern during actual use. Tony, How about fitting a sensor on the pattern plate and (using a PIC of course) measure the time difference between the first hit and the last. This would give you an indication of the length of the shot pattern, given that you know roughly what the velocity is. Hell, put a sensor on the muzzle and we could even check the velocity. Hmm, I wonder how they'd feel down the club if I turned up with me gun and a box full of electronics? Philip Martin. In actual use the spread of the shot is also modified by the moving barrel as you track the target. Therefore as well as knowing where the passes through an XY plane perpendicular to the gun barrel you also need to know when it passes through that plane. I would suggest that the only practical way of obtaining this information is to record the shot passing through a light curtain with a high speed camera, digitising the results, then comes the easy bit, mathematical modification to simulate the effect of the moving barrel. Chris -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.