Chrono on handloads not matching up with truing

[schiffer99]

Been working up a 6.5 creedmoor handload for a while now. Came up wiht a Barnes 127 grain LRX load over StaBall that is shooting lights out. Ready to take it hunting next week for mule deer and went to the range to confirm the longer distances.

I started by confirming my 100 yard zero. I then ran a couple rounds through the chrono, pretty consistent around 2,840 feet per second. Took that info to the long range steel range using the Horus App. (I have a TREMOR 3 reticle.) I am shooting a 18' barrel sig cross (suppressed), so I think this is a pretty hot load.

At distance the shots were sailing high when using the range card the app spit out base upon my inputed muzzle velocity and BC. (I digiscope recorded each shot and could see where they were going.) For a 550 yard shot it said the hold should be 3.3 mils: shot high. I dialed down to 3.0 mils and got point of aim point of impact. Same result when I dialed back to my zero and held 3.0 mils in reticle. At the 420 yard steel the card said it should be 2.3 mils, but the hit hold ended up being 2.0 mils.

Using the truing application on the Horus app it wanted to change my starting muzzle velocity to 2,912, which is a 70 ft/sec increase from what my chrony was reading.

I'm leaning towards to rolling with that as the bullet doesn't lie... but before I trust that on live game I wanted to check to see if I'm missing something obvious.

 

[Wrench]

Have you tall target tested the scope?

You have two impacts coming in .3mil off....100 is guaranteed to be zero?

 

[schiffer99]

Have you tall target tested the scope?

You have two impacts coming in .3mil off....100 is guaranteed to be zero?

I have not done the tall target test..... BUT your mention of scope high made me wonder if I input the scope height over bore correctly. My original input was 1.93 inches, I just measured and came up with 2.7 inches. I input that height and reran the numbers and now everything seems to be matching, or at least very close.

(Not sure why I was off. Only theory is I did the measurement when I had a different scope on the rifle.)

 

[Tex_F15]

 

[Harvey_NW]

I just measured and came up with 2.7 inches.

2.7" seems excessive, this article explains how to get it very close and also notes that most load manuals and ballistic calculators are set at 1.5" as a common standard, I always start with 1.7" on Strelok. I've also always trued BC and MV on my calculator by shooting at doubling ranges like 400 and 800, and then adjust the numbers accordingly based on impacts. May not be the correct way but it's always worked for me, and my velocity is almost always within 20fps of my chrono speeds.

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[XLR]

Truing Rifle Data

This is the time of the year when shooters start getting the itch. It is the best time to start brushing up on your wind calls and making sure that your rifle is shooting well! One common question that we get asked is how we true our data when we gather dope. This is a great question because...

xlrindustries.com

Here is an article I wrote a little while back that could be beneficial for ya! Before you start shooting though I would get the correct ring height. I have always done barrel diameter/2 + gap between barrel + scope bell/2. I would say 2.7 is probably about right with the cross, it has a super high base compared to tikkas/Remingtons. With that being said I know my 700 with an EGW base and a 1.5" spuhr mount I am right at 2.5. Measure and make sure though so you aren't scratching your head at the range.

 

[BRTreedogs]

Chrono does not take into account the effect of wind at distance.
If you had a tail wind it could cause you to shoot high if you did not input direction and speed correctly into the app

 

[BjornF16]

What chrono?

They are not all created equal...

As OP replied, variables also need to be correct in the ballistic calculator...like scope height over bore.

 

[Travis Bertrand]

I echo what some others have said...
What Chronograph? and you shouldn't adjust your speed in Horus. adjust BC.
make sure gun Is zeroed, close Height over bore, and speed.those things are known right? shoot close to transonic and adjust BC on that.

 

[Travis Bertrand]

also, my sig cross has a 2.65 or so HOB for what its worth. That is with my daughters 56mm Burris on it. It could be lower with different rings but not much lower.

 

[schiffer99]

Chronograph is pro chrono pal. I would call it serviceable, seems to be where I expect it to be though it has issues when its super hot outside.

I have Leupold Mark 5 that is sitting in an ADM Recon mount (this scope jumps to a couple of my AR's as well) so it does sit a lot higher than most. I whipped out the calipers, and was getting around 2.55 to 2.6 HOB, which I think should be good enough.

I will go out again this weekend to make sure everything is matching up and to work on positional shooting. Still a little nervous as I will be going from 85 degree and 1,800 altitude Tucson to like 30 degree-ish and 5,200 altitude on the hunt. But, I have a self imposed limit of 400 yards under ideal circumstances, so if I'm nailing at 550 at the range I should be good. (Please knock on wood for me, I just did.)

 

[jzeblaz]

Sounds you've got it figured; Always good to verify. Whenever I am up against the clock like that and stressing long distance, I draw a gimme shot. Good luck on the hunt and report back your findings and success.