243 Win - More Powder gives lower Velocity - Why?

[RonAKA]

I'm trying to help a friend with getting his 243 Winchester to group. He's using H4831 powder and 100 grain bullets. Following is the resulting velocity (Chrony Alpha Master) from a two shot per load ladder test. The magenta line is the Hodgdon minimum load and maximum load data points for H4831.

What do you think could cause the drop in velocity in the middle of the load range tested? There is one really low velocity that I believe must be an error with the chronograph, and suggest that needs to be ignored. I don't have a graph to show it, but the elevation of the POI follows the drop in velocity. The exception is the one really low reading. It is close to the other of the same load, which suggests the velocity of that one point is an error.

I'm puzzled? Have you seen this before?

 

[Beau]

Could have been a bad primer.

 

[Kenny474]

I have no real insight, but I would try the exact same test again and see if results are duplicated.

 

[jo191145]

I'm using the same Chrono right now. Very tempermental little gadget compared to my old unit.
I've seen all sorts of wierd velocity readings with it. Super high, super low.
My bench is in the shade. I've found the bullets need to pass right over the eyes to work. If the sun makes its way through the canopy it can send it haywire. I usually take a five minute break and the sun beam will move.
I wonder if I shot in full light maybe the bullets would need to be higher over the eyes.
Weak battery will mess with it also.

If the bullet did'nt drop like a rock I would disregard the data. Looks like 2875 is a flat spot.
What did the accuracy look like?

 

[OKIE2]

Maybe you need to change powder
Try this it works for me