I shot a few rounds today and I got numbers which seem a little hi based on published load data and was wondering how do you check if your chrony is right? New battery in my Master Chrony. 24" Barrell length on all three rifles Here are the numbers I got:

257AI 120gr Nosler Part 48.5gr N160
3159
3130
3168
3157
3169

300 Wthby 180 Nosler BT 84.5gr IMR7828
3549
3529
3565

375H&H 300gr Hornday SP
2837
2848
2785
2846
2845

The obvious way is to find someone who has a different chrono and run side by side tests. Your readings look good and uniform, but if thoses numbers are correct (and I see no real reason to think they're not), that 375 must set back just a bit!

Make sure the Chrony is opened up flat after you fasten it to a tripod. Your 2800 fps with the .375 and 300-grain bullet ie way high. I have had this happen before, had it opened up flat, accidentally bumped it when leaning over screwing it onto a tripod. If I get one silly reading, I check it immediately.

If you are going to check your readings using a second chrony, set one ahead of the other so that you will get two readings from one shot.

Ok, so if you don't have two chronos? If you have a known consistent load, I use .45acp match ammo, fire that over the screens to check. I agree, 2800fps w/ a 300gr/.375 , wow!

Sometimes sunlight will reflect off of the bullet and affect the reading. Try a sunshade. reorient the Chrony, or try a different time of day.
Good Luck!

I forgot to add; Sometimes the muzzle blast from slower powder will cause an off reading.
The check is to shoot at 10', then at 15' and compare velocities.
Good Luck!

Hawkins has a good point,
If I shoot after 10:00am in sunlight I always get high readings,I think it is the angle of the sun on the sensors.

Sean

Maybe it's just me but you 300 Whthby load seems a bit hot 7.5 gr above Nosler #4 book max and 4.5 above Speer.

I can't tell you anything about your .257 or .300 W. M. loads, and you forgot to give us the load you are using in the .375!

However, I doubt that you are getting anywhere near 2800 FPS with a 300-grain bullet in the .375 H&H!

The wthby max load for IMR 7828 is 86gr according to my 300 wthby load manual.

I agree they all look suspiously high and the primers were not flat. The Ackley I was expecting around 3000, the wthby around 3200, and the H&H around 2500, so I knew something was not quite right. The question is when can I believe my chrony? The standard deviation looks good, so I have consistant readings that are high. It was a cloudy morning, I did not use the sun screens. I think there may be some merit to making sure the chrony is opened up flat. Next week I will try with the chrony open flat and then close it up a litte to see if my results change.