This might be a stupid question but I have been noticing a trend recently on load development and then subsequent rounds sent by a chronograph. I have been handloading for 10 years+ not saying I am an expert, but not a newbie. As I chronograph more than I used to and gather more data this trend has emerged more frequently. It has happened on other cartridge's, bullets, powders and rifles, and a buddy has been seeing the same thing. Hopefully there are some here that can explain why it happens and how to mitigate it.
I am loading on an A&Dfx120 scale and calibrate it before use. I also have a bullet with a known weight sitting there to check occasionally during loading for consistency of what it shows for that bullet. The powder pan is also a good check for if scale drifts at all. So I feel like my powder drop is accurate to the resolution of the scale. I am especially picky on what I dump for load development vs. a match
What I see is shooting in the morning I am getting velocities somewhere between 30 & 50 fps slower than if I shoot in the afternoon. Same load, same seating depth etc. I can't imagine it is ammo temperature as in these cases I am loading up a ladder or later in load development larger strings in a temperature controlled environment, walking out the back door and shooting them within a few minutes, 5 or 10 max.
Example: 6 GT, Alpha brass, 112 match burner jumping .070, N555, Lab Radar for chronograph.
-Sunday afternoon: 46 degrees calm and sunny 38.1 grains was running 2875-2880 SD of 5
-Monday morning: 30 degrees light breeze 38.1 grains running 2830 with SD 3 and in the .3's
-Monday afternoon (same day): 42 degrees similar breeze, 38.1 grains back up to 2880. This time I ran 19 rounds over LR and had an SD of 8 which is expected with a larger sample size, first two groups were lower round count, lower SD may have been skewed.
I was shooting from same position with the lab radar set as consistently as I can get in relation to muzzle and target alignment. So is this an inconsistency in the Lab Radar from one session to another? If so why is it always faster in the afternoon? Ammo temperature seems unlikely where it is shot so quickly after loading. Externally is colder air and lower barometric pressure in the morning a cause? Just trying to figure out if it is something that can be eliminated, or just have to live with it? Maybe it is bad data and velocities aren't that far off, but then how can you trust a lab radar?
I am loading on an A&Dfx120 scale and calibrate it before use. I also have a bullet with a known weight sitting there to check occasionally during loading for consistency of what it shows for that bullet. The powder pan is also a good check for if scale drifts at all. So I feel like my powder drop is accurate to the resolution of the scale. I am especially picky on what I dump for load development vs. a match
What I see is shooting in the morning I am getting velocities somewhere between 30 & 50 fps slower than if I shoot in the afternoon. Same load, same seating depth etc. I can't imagine it is ammo temperature as in these cases I am loading up a ladder or later in load development larger strings in a temperature controlled environment, walking out the back door and shooting them within a few minutes, 5 or 10 max.
Example: 6 GT, Alpha brass, 112 match burner jumping .070, N555, Lab Radar for chronograph.
-Sunday afternoon: 46 degrees calm and sunny 38.1 grains was running 2875-2880 SD of 5
-Monday morning: 30 degrees light breeze 38.1 grains running 2830 with SD 3 and in the .3's
-Monday afternoon (same day): 42 degrees similar breeze, 38.1 grains back up to 2880. This time I ran 19 rounds over LR and had an SD of 8 which is expected with a larger sample size, first two groups were lower round count, lower SD may have been skewed.
I was shooting from same position with the lab radar set as consistently as I can get in relation to muzzle and target alignment. So is this an inconsistency in the Lab Radar from one session to another? If so why is it always faster in the afternoon? Ammo temperature seems unlikely where it is shot so quickly after loading. Externally is colder air and lower barometric pressure in the morning a cause? Just trying to figure out if it is something that can be eliminated, or just have to live with it? Maybe it is bad data and velocities aren't that far off, but then how can you trust a lab radar?