I have been chronographing some reloads trying to duplicate some factory velocities. In my past experience chronographing pistols & rifles, we always placed chrono screens @ least 10 ft from the muzzle to avoid muzzle blast. My results were a little less than that published. Now I am aware of all the variables involved with factory testing and it would be difficult to duplicate exactness. I read somewhere recently where chrono testing was done 3 ft from the muzzle. This seems to awful close to the muzzle even for a shotgun. Please enlighten me as to how the factory does it and how I should do it?
The US standard for chronographing is three feet from the muzzle, but it is also to the center of the mass of the shot cloud. “Home” chronographs, like yours and mine, measure the lead pellet. The difference really isn’t that much so you shouldn’t lose sleep over it the way I do. I’ve been slow to move the chronograph further out as I am concerned that a flyer might hit it. I’m sure that your aim is better.
I was concerned about muzzle blast on my ProChrono’s front plastic LED readout, so I stuck a thicker piece of plastic over it. Worked fine. My chronograph is quite sensitive to ambient light and light angle, at least that is what I think the problem is when I sometimes don’t get consistent readings. It could be muzzle blast. Moving the chronograph further out (and holding tighter) is worth the experiment.
Do remember to accurately measure the distance from your muzzle to the center between your chronograph screens to get consistent results. The difference could be a couple of feet per second. That really matters, right?
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)