I just bought a Chrony but if it don't work I may Holler BackI second the Magnospeed. They also have what they refer to as a "Large Brake Adapter", so that may work also.
The Sporter model is very reasonably priced. PM me and I can refer you to a reliable retailer with very good pricing.
I've always wondered why they say you cant use fluorescent lights thanks for letting me know about this I'm learning something every dayYou would need to be sure that your light source (e.g. LEDs) would be constant and not pulse. For example, fluorescents pulse at either 60 or 120 Hz. We can't see it because of the latency of our eyes. If the power supply for the LEDs were not pure DC they might be strobing and you wouldn't know it. How much light you need is also another issue. Some chronograph manufacturers (e.g. CED) make lighting units specifically for using their chronographs in the dark.
Just came in from tuning some loads here at night... love the mag speed!!You could just purchase a Magneto Speed it operates on magnetic pulse and can be used in total darkness. If you're using a muzzle brake designed like field artillery piece it probably won't work.