I would assume the lighting would have something to do with your gain. I talked to a friend about this subject awhile back (not your particular experience
) that has many miles more experience than I, and he said that he has had the lower end chronographs (chrony is one of them, if you want to argue about it find someone else) react extremely sensitive to light and shadow. He gave a few interesting examples in our conversation that are very pertinent. One would be, while working up a new load for a .222 Rem with a 55 grain Sierra he was trying H322, a powder he had not used in this cartridge before. He was working up to a recommended maximum, as recommended
, and about 2 grains short of 'maximum' he was suddenly clippin' those .222's along at 3400 fps! He shot twice more quickly and had readings within 50 fps of the last. Now being that .5 grain earlier he was only getting a 2800fps reading he found this quite odd. In fact he said he would have questioned whether he had used the right powder or not, except that was the only cartridge he was loading at the range that day, and the only powder he had with him was a single can of H322. Accuracy had even improved with this increase, so he assumed maybe, just maybe he had best let the gun sit and he should load a few more rounds with the same charge of powder and and try a different 'mean' rifle over the chrony to see if his senses where still with him. When he came back it was that perfect time of day for shooting. The range he was at was in the mountains, and the sun had just hit the trees and all movement in the air had stopped. He first shot his pet 7x64 Brenneke over the chrony and sure enough his old standby 154gr Hornady load read 2900fps over the chrony three times. So he imagined that some how, some way he had discovered a magic combination of brass, primer, powder and seating depth for this particular bullet. So he settled in and shot those those 'magic' cartridges. To his suprise the untampered chrony reread these rounds at shy of 2900 fps. Six times. That was a 500fps difference! How this could've happened only God knows, but the man I heard this from was an unexcitable fellow, prone to underestimation and belittling his own experiences (he once said that he was going to the hospital for some treatment....six months later his knee replacements had healed fully and he was climbing his beloved peaks again
). He could not believe that his eyes had lied to him so, and due to intelligent reasoning and experience he tried the same load the same time of day the next day, as he understood hoe the chrony functioned (when he goes to the range, he takes a trailer, and a couple hundred rounds with appropriate rifles, as good things should never be rushed
). He had a similar problem the next day, yet not as extreme, and the Brenneke reacted as well. The chronograph in this case was his first ever, and happened to be a Chrony Alpha, and he has since invested in a Oehler.
I would definately question 3750fps as safe. But then again, you may have found that 'magic' combination some people think they have whrn the push a 300 Winnie to 3200 with a 180grainer. Only you will ever know
.
