I wasn't jumping all over you, sorry if it seemed that way.
It's just that what you said about the correlation between distance and standard deviation made no sense... SD's relate to one's "cone of fire" only, there's no real reason to chrono every round unless one has a magic chrono that tells the future.
The issue is that cone really isn't a cone, it's more akin to a bell of a brass instrument. The farther out you go, the more it "bells" out.
About a month ago, I was shooting my 37XC:
It was not a good day from the get go. My rangefinder wasn't even close to picking up the target. I had to walk about 600 yards out before I could get a reading. I then turned and got a reading off my Jeep. The problem was, I was walking downhill, and the target was up. So, I didn't have a linear distance - it was a shallow triangle. I had to make an educated guess and came up with 2400 yards. I took GPS readings from my Jeep's built-in when I picked up the target and calculated the distance when I got home. It was actually 2504.
That was variable #1 - and my next investment is likely a Garmin handheld.
The terrain is quite hilly and the wind, while relatively light, was shifting direction constantly.
That was variable #2.
I expect about a 5-6 SD with this load in this rifle. It was not that and I had a ~30 FPS ES
That was (unexpected) variable #3.
The first shots were painful. Just spotting them was difficult. But then, once I got on target, it was hell keeping consistent. I'd drop one low, adjust, then go high, adjust, not spot the next one, etc. What was causing these misses? Was it the bell effect? Was it the wind shifting to more head-on vs. side? Was it me not managing recoil consistently?
Without understanding what is causing the variations, you're just guessing. By checking the velocity each shot, that eliminates one of the variables. Without the chrono on each shot, I would have been chasing misses all day long. At like $4-$5/shot, I'm not too keen on doing that.
By contrast, last weekend I was shooting it at 1900 yards. Aside from the fact that the backstop was wet, clay-like dirt that just ate misses, the consistency was there - and 1900 with the 37XC is very different than 2500. I'm still learning the rifle and round, but it was clear that at this range it hadn't hit the bigger part of the bell yet, while (ammo issues aside) at 2500 it at least was starting to.
With the 2500 yard shots, once I got on target, the first variable (unknown exact distance) was eliminated. Wind is always there and variability can at least be somewhat reduced by anticipating it correctly. The variability due to ammo deficiency can only be somewhat overcome by looking at previous rounds.
