I am admittedly a newbie with both PCP rifle (25 Marauder) and chronographs, so please bear with me.
I borrowed a friend's Pro Chrony (a few years old) and set it up on a bench in my unheated garage for the winter.
The rifle was set up on a bench rest tripod and sandbag and returned to approximately the same position for each string. More on this later.
Having read about the potential issues with fluorescent lights, a desk light with incandescent bulb was positioned above to shine down on the unit. The diffusers were installed - I could not get readings without them. While shooting the overhead fluorescent near to the chronograph was turned off.
Readings were IMHO relatively consistent for quite a while and trends made sense.
I had just installed a new Hill kit + Huma regulator and was running short strings every few days to assess the tune and consistency over time. It is noteworthy that the temperature was dropping as winter set in, but I kept the rifle, pellets, and chronograph in heated area until shooting. A five shot string only took a few minutes.
Velocities were running ~ 885 fps with ES < 1%. Then during one string I began to get flyers down to the low 800's - and this was on an unseasonably warm day. I was aware of the number of consistent shots per fill so this wasn't an issue. I took rifle back into heated area and tried later. The subsequent string was consistently in the low 800's. I was planning to do some outside shooting at distance, so cranked spring back up to again achieve 880 fps.
Quite a few days later I shot another 5 shot string and velocities were 906, 1036 (!), 906,905, 814, 905, 814, 809. WTF? I recalled that I had 1048 fps previously, but ignored it at that time.
So now there are both low and high flyers and doubt that both are possible. I can understand the lows, but not the highs.
Subsequent investigation and conclusions:
The alignment of the chronograph to the rifle was not precise enough nor repeatable enough. This was found to contribute to low flyers.
On a whim I placed a white poster board under the chronograph and shot a string with it upside down on the posts (like a Caldwell) without diffusers. Readings were consistent, but 80 fps lower than the last string. The chronograph was then flipped over (still on white poster board), diffusers reinstalled, and an additional light was added - one above each diffuser rather than one in the middle. With more precise positioning, reading are now again very consistent with those taken with unit upside down and trends again are making sense. The reflected light from the poster board may be beneficial. We shall see.
The high flyers are still a puzzle.
I borrowed a friend's Pro Chrony (a few years old) and set it up on a bench in my unheated garage for the winter.
The rifle was set up on a bench rest tripod and sandbag and returned to approximately the same position for each string. More on this later.
Having read about the potential issues with fluorescent lights, a desk light with incandescent bulb was positioned above to shine down on the unit. The diffusers were installed - I could not get readings without them. While shooting the overhead fluorescent near to the chronograph was turned off.
Readings were IMHO relatively consistent for quite a while and trends made sense.
I had just installed a new Hill kit + Huma regulator and was running short strings every few days to assess the tune and consistency over time. It is noteworthy that the temperature was dropping as winter set in, but I kept the rifle, pellets, and chronograph in heated area until shooting. A five shot string only took a few minutes.
Velocities were running ~ 885 fps with ES < 1%. Then during one string I began to get flyers down to the low 800's - and this was on an unseasonably warm day. I was aware of the number of consistent shots per fill so this wasn't an issue. I took rifle back into heated area and tried later. The subsequent string was consistently in the low 800's. I was planning to do some outside shooting at distance, so cranked spring back up to again achieve 880 fps.
Quite a few days later I shot another 5 shot string and velocities were 906, 1036 (!), 906,905, 814, 905, 814, 809. WTF? I recalled that I had 1048 fps previously, but ignored it at that time.
So now there are both low and high flyers and doubt that both are possible. I can understand the lows, but not the highs.
Subsequent investigation and conclusions:
The alignment of the chronograph to the rifle was not precise enough nor repeatable enough. This was found to contribute to low flyers.
On a whim I placed a white poster board under the chronograph and shot a string with it upside down on the posts (like a Caldwell) without diffusers. Readings were consistent, but 80 fps lower than the last string. The chronograph was then flipped over (still on white poster board), diffusers reinstalled, and an additional light was added - one above each diffuser rather than one in the middle. With more precise positioning, reading are now again very consistent with those taken with unit upside down and trends again are making sense. The reflected light from the poster board may be beneficial. We shall see.
The high flyers are still a puzzle.
