Interesting Session With Chronograph

[amlevin]

I always wondered how close the "results on paper" would correlate to the best "statistics" generated from a "chrono session".

Friday I put it to the test. Loaded a series of rounds in .4 gr increments using IMR-4064 and 168 gr Hornady A-max bullets. Shot the series at 200 yards so I could could sort out a really good group easier.

Cases were all previously shot and even in all aspects of prep. Primers were BR-2.

Starting load was 42.3 gr and last load was .1 gr less than published max. All bullets were seated just to the lands. The starting load was enough to keep soot from covering the outside of the neck and not a single pressure sign at the ending load.

Here's the chart I generated from this series shot over the chronograph.

Found it very interesting that the best groups were at 42,7 gr, 2636.2 fps avg (a "bughole") and 44.7 gr, 2759.9 fps avg. (<1/2"). These groups coincided with the dips in SD, MAD, and ES.

Maybe the chrono stats DO mean something

FWIW, with Varget's new formulation shifting to Unobtanium, IMR-4064 is becoming my "new best friend" 8) Wonder when a boatload of Varget is due next?

 

[jo191145]

And I've shot a 5 shot 0 group at 100 yds with a 200fps spread.
I know every theory in the shooting world says that's impossible.

 

[amlevin]

And I've shot a 5 shot 0 group at 100 yds with a 200fps spread.
I know every theory in the shooting world says that's impossible.

I'd see that possible in 100 yards but what about extended ranges when speed variations tend to have more effect? That's why I do load development at 200 and 300 yards now. I didn't learn that much with a whole target full of "bugholes" at 100 yards.

 

[jo191145]

I agree with the yardage. There are other factors that come into play. Weight and velocity have a great effect.
My home range is either one or two hundred yards. Seldom shoot at 100 myself. The only time I see any use for 100 is winter and windy when I feel going to 200 would sway the results worse than not getting all the results at 100. Or I'm shooting something relatively inaccurate anyway. Either way it's more of a joy of shooting thing than discerning a few thousands in group size.

 

[mikecr]

Thanks for testing & posting results amlevin
I've never tried this myself. I wonder if your results would follow -while at best seating depth.

 

[amlevin]

Thanks for testing & posting results amlevin
I've never tried this myself. I wonder if your results would follow -while at best seating depth.

That's actually my next step. Today I'm heading to the range to test the two "accuracy nodes" that appeared on the first "sweep" and if they repeat (not science if they don't), I'll start testing the seating depths, recording every shot on the chrono. This is when it's nice to have a printer incorporated into the Chronograph.

 

[Joe R]

Looks potentially interesting but, I don't understand what the Y-axis represents.

Joe

 

[mikecr]

Y = velocity variance (ES, SD)

 

[jcinsa]

Hey Amlevin,

On your graph, what does MAD stand for ?

Can't guess what it could be.

Thanks

John

 

[amlevin]

Hey Amlevin,

On your graph, what does MAD stand for ?

Can't guess what it could be.

Thanks

John

Mean Absolute Deviation or as some might also say Mean Average Deviation.

Essentially the the average of each shot's deviation from the overall average.

In some ways this can be more meaningful than both ES or SD. If you have a MAD of 5 fps and at the range at, one fps of speed variation means one inch of elevation, then statistically each shot will hit from 2.5" above to 2.5" below the target center, all other things being equal.

 

[sbhooper]

With heavy rifles, I definitely agree with longer range testing. I have noticed, however, that I can get tiny groups at 100 yards and upon moving out to 300, my groups stretch because of me being more unsteady with the light rifle. I am splitting hairs, as I am talking about the difference from 1/2 minute out to 3/4 or one minute, so unless you are a bench-rester, it is not a big deal.

I believe that tuning the load at 100 and then moving out to check results is the way to go for me.

 

[jcinsa]

Ah ha!

So that's what it means ( no pun intended )

Thanks

 

[CPorter]

From your chart I would expect the 42.7 grain load to be temperature sensitive and the one at 44.7 to be much less so. Have you noticed anything like that?

 

[amlevin]

From your chart I would expect the 42.7 grain load to be temperature sensitive and the one at 44.7 to be much less so. Have you noticed anything like that?

Not sure I could draw that conclusion myself unless you feel that the chamber temp was affecting the higher weight charges which were shot later in the sequence. FWIW, I don't sit with a round chambered any longer than necessary to acquire target and pull trigger. If there's a delay, like waiting for wind, etc, I'll unchamber the round and let it sit on the magazine follower, closing the bolt when all is ready.