I have Pro chrony digital brand chrono that I have owned for about six years or so, I used to do most of my chrographing between nine and eleven in the morning and used to set it up where the rods that hold the diffusers would create a thin shadow over the photo eyes but stopped using that method because due to the suns moving I would have move the chrono every five minutes or so in order to keep the shadow in the same place. I decided to just point the chrono northeast and it worked very well untill a few months ago wen I started to get multiple readings on five shot strings, some times the first and third shot would read the same,some times the second and fourth shot were the same. I tried shooting later in he morning after eleven and that seemed to have cured the problem.
A few weeks ago I was chronographing some loads and the first three loads were reading fairly consistant, the last two shots read about fifty fps faster, I went to check the chronograph and noticed that the shadow created by the difusers was almost touching the photo eyes, usually the shadows are about two inches in front of the photo eyes. I tried an experiment and shot a string with the shadows in front of the photo eyes like I normaly do and then moved the chrono so that the diffusers were shadowing both photo eyes, with the eyes shadowed the average speed was 36 fps less, I was chronographing 223 loads. I called the company and talked to a tech and asked which readings were correct, he was not sure but the readings with the photo eyes shadowed are probably the more correct readngs. He suggested putting a piece of card board or white typing paper over the diffusers that way I have a shadow all the time.
I went out earlier today and was chronographing some rimfire loads using the method with the shadows in front of the photo eyes, I chronographed some rounds using my Winchester model 62a, they were averaging 1182 fps, took my Ruger 10-22 and chronographed the same rounds, the Ruger waa averaging 1208 fps, my 62a has a barrel that is longer than the Ruger and has always produced on the average about 30 fps more speed than the Ruger. I then left the chronograh in the same position and fired some rounds again using the 62a, the rounds were averging about 35 fps faster than the first string, I also noticed that the shadows were almost touching the photo eyes. My question for anyone who is an expert with chronographs is what should I do to if anything to keep the readings consistant. My main concern is that I have some handloads that are near book maximum and if the chronograph is not reading correct some of these loads may be sligtly over max or under, any help is appreciated.
