Lessons from a verification shoot

I've been enjoying time with my howa in 7.62 x39 recently it's now my go to pest rifle. I had fitted it with a nikko stirling gameking 3-9 half mil dot and found it ticked the boxes out to 400 for holdover with a 150 yard zero. Anyhow it suffered a serious accident Saturday so I fitted a spare weaver with bdc zeroed it and having no idea of what the bdc units were decided to shoot a verification ladder.
I finished the ladder and started measuring the drops, all were within cooee of the predicted results except 250 which was 2 1/2 inches high. I reshot it same result, confused and out of options I decided to remeasured the firing points. My 250 mark was actually 237 yards and has been for ages, I don't normally use it so I checked all my others and they came out within 2 metres of what they should be except the 300 that was 308 yds.
Simple mistakes can sometimes trip you up.
Anyhow here's the ladder
The 350 yds shot punched a hole in the pallet the target was so pinned to just below the cardboard and the 400 ploughed the dirt 6 foot in front.

That is interesting, wish this was posted a few months ago. I have recently had some issues validating a drop chart, things just didn't work out, and had no real explanation until side by side with another rangefinder, my up till recently very reliable range finder(PRF) was now not providing accurate readings.....suspect it had been happening for a while, but never thought to re-check the ranges or equipment.
Cheers

The bulletdrop doesn't lie. Amazing how small errors can change the results. At least you got it sorted ok.