Shotmarker odd question about ave. velocity

[r bose]

Shot the last 2 weekends at 600 yards using the same 2 rifles, loads, projectiles, etc. Everything the same

Weather conditions just about identical, hot and humid here in SE Louisiana, not more than a degree or two different. Not enough wind either weekend to be moving the targets around or disrupting any of the shotmarker readings.

We used 2 different Shotmarker systems independent of each other. 2 different 600yd ranges. SD was spot on over a 20 shot string for each of the shotmarkers BUT, the average velocity was almost 100FPS more on 1 system over the other.

How does that happen and has anyone else experienced this?

 

[Walt Krafft]

Happens all the time. The velocity is not calibrated to give an accurate speed.

 

[Steveb]

If you shot on 2 systems, did you use separate target boards? If you did, what is happening is the dimensions for the spacing of the sensors is slightly different between each target setup. I have exactly the same thing happen to me recently. Our match targets use machine aluminum frames where the sensors are all within 1mm in all dimensions while we use wooden frames for practice. The practice frame sensors are located sort of precise. The velocity difference is over 100 fps between the frames and it is repeatable.