This is just a warning to those who (like me) might put too much faith in their cheap Caldwell Ballistic Precision chronograph. You might say "well obviously it's a cheap POS based on the price" but I have trusted it for many years and it was good enough that I didn't really notice a major issue. Maybe others also have this issue with other chronographs as well, I don't have any experience with anything else.
Basically it detects different velocities based on where in the "detection area" I shoot, based on my point of aim. If I aim at a target which goes through the upper portion of the chronograph, that group will show a pretty good SD/ES. I then shoot the same exact load/rifle combo at a different part of the same target, which might go through the lower portion of the chronograph, and that group will also show similar SD/ES BUT a very different average velocity.
For example:
Group 1 shot at top left of target
2555 ft/s AVG
23 STDEV
51 ES
Group 2 shot at middle of target
2600 ft/s AVG
23 STDEV
56 ES
Group 3 shot at bottom right of target
2502 ft/s AVG
12 STDEV
31 ES
Calculating all groups together as one data set
2552 ft/s AVG
47 STDEV
152 ES
You can see that within each group, the SD/ES is pretty consistent. Taking all velocity values of the 3 groups and doing the math as one set of data makes the load look awful. I can shoot 5, 10, or 20 shots at the same point of impact and get similar average velocities. As soon as I change point of aim (bullet crosses chronograph at a different location) I get a shift in velocity.
Waiting for the Caldwell VelociRadar to be released before I decide whether I want one of those or a Labradar.
Basically it detects different velocities based on where in the "detection area" I shoot, based on my point of aim. If I aim at a target which goes through the upper portion of the chronograph, that group will show a pretty good SD/ES. I then shoot the same exact load/rifle combo at a different part of the same target, which might go through the lower portion of the chronograph, and that group will also show similar SD/ES BUT a very different average velocity.
For example:
Group 1 shot at top left of target
2555 ft/s AVG
23 STDEV
51 ES
Group 2 shot at middle of target
2600 ft/s AVG
23 STDEV
56 ES
Group 3 shot at bottom right of target
2502 ft/s AVG
12 STDEV
31 ES
Calculating all groups together as one data set
2552 ft/s AVG
47 STDEV
152 ES
You can see that within each group, the SD/ES is pretty consistent. Taking all velocity values of the 3 groups and doing the math as one set of data makes the load look awful. I can shoot 5, 10, or 20 shots at the same point of impact and get similar average velocities. As soon as I change point of aim (bullet crosses chronograph at a different location) I get a shift in velocity.
Waiting for the Caldwell VelociRadar to be released before I decide whether I want one of those or a Labradar.
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