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Chonograph speed vs scope dial up at 600yards

This is not a solution. I have seen more guys twirling kestrels at matches like "tactical fidget spinners" and still missing targets. Shooter, JBM, AE, Strelok, Etc, will all give you good data if you if you use them properly.

Also the sight height is not going to effect as much difference as you posted. A bad zero however will screw you up. My money is still on environmental or bad input.
A scope that doesn't track true MOA will do it. Need to do a tall target test at 100 yards. Matt
 
Yup, I've gone over all the variables again and get 11.4 MOA also.

I need to run the remaining loaded rounds from that match and verify the chonograph numbers again. It was around 70 degrees when I ran the load against the chon and 45-55 degrees during the match. That should not make 85 fps drop would it?
I tested powder in temps by testing real temp verses temp from shells in a cooler. Even though the powder I was using was supposed to be the best for temperature differences, 20 degrees gave 50 feet per second difference. It was 70 degrees verses 50 in the cooler. This was with a Dasher. Matt
 
The scope is a Sightron 10-50x60. Fine crosshair, Target dot 0.1 MOA reticle. Should track in MOA right?
I assumed it was MOA becuase thats what I use. I forget about Mils. You just need to check it and make sure it's tracks true. Wouldn't have to be off much to cause a lot at 600. Matt
 
I tested powder in temps by testing real temp verses temp from shells in a cooler. Even though the powder I was using was supposed to be the best for temperature differences, 20 degrees gave 50 feet per second difference. It was 70 degrees verses 50 in the cooler. This was with a Dasher. Matt

This could account for some on the dial up difference. Defiantly a colder day, than when I did my powder OCW with the Magna Speed installed.

32.0- 32.1g of Varget was giving me close to 2900 fps, 32.8-32.9g was avg 2985fps and shot well. 2900fps was between nodes and had scatter. If I was truly at 2900 fps as my dial up indicated in my match, I was "out of tune".......sigh.
 
The dominant effect of temperature is on the density of the air you are shooting through, not the velocity. I ask again, do you know you are inputing accurate BP and temp when you are shooting?
 
No one has mentioned yet that there is an error band on the velocity we read from our chronograph. Take the specification stated by the manufacturer and see how much off your velocity could be within that band and see how much that could contribute to the difference you are seeing. That may not explain all the difference but it is one factor.
 
BT the BP is a major variable. Smart phones have a built in probe which many ballistic apps can access for accurate, real time input. Or you can get a free app to display it for you. If you guessed using reported BP then this could easily explain the error; read up on weather BP vs station pressure which is the actual to use. This is a frequent learning experience!
 
This year one of my goals was to learn to use my app correctly. I realized the only way this would work was to input every detail correctly leaving nothing as a guess to the best of my ability. I purchased a kestrel as well and in my opinion that was a huge plus. A couple things I have learned is you must record your zero conditions in the app and save them and input the shooting conditions at the time of shooting that day , the app will compensate for you at that point provided the data you input that day is correct. You MUST have a true zero as well. I also true my speed at 1000 if I feel my speed is off( the target doesn’t lie). Once I started inputting actual data I started making hits at distance on a much improved ratio and my misses are much closer than before. The old saying garbage in garbage out is soooo true. Check your zero and input actual conditions for the day and I bet you will be just fine. Good luck. Troy
 
I'm with CharlieNC. You could switch to Density Altitude in Shooter and use that single "DA" number for environment (Alt/Baro/Temp/Dew/Humidity). I have a cheap kestrel that gives me DA. With that, I 'm usually good. I would suggest you verify your dope again JBM Online and see what JBM tells you. Your barometric pressure is likely wrong. Barometer also has 2 different options, "Adjusted for altitude" and not adjusted aka "Station Pressure". Adjust Barometer will always be 29.x inHG, like you see on the weather forecast. Station Pressure (not adjusted) will be lower. Here in Colorado our Barometer will read 24.x. If I use the wrong one I will be way off, even though the rest of my data was correct.

Also if you give me your data I can run it for you and see what we get. If the ballistic data is right/wrong, maybe we can rule that out and look at scope, zero, etc to help you solve what is happening.
 
BT the BP is a major variable. Smart phones have a built in probe which many ballistic apps can access for accurate, real time input. Or you can get a free app to display it for you. If you guessed using reported BP then this could easily explain the error; read up on weather BP vs station pressure which is the actual to use. This is a frequent learning experience!

will do. Thank you!
 
I'm with CharlieNC. You could switch to Density Altitude in Shooter and use that single "DA" number for environment (Alt/Baro/Temp/Dew/Humidity). I have a cheap kestrel that gives me DA. With that, I 'm usually good. I would suggest you verify your dope again JBM Online and see what JBM tells you. Your barometric pressure is likely wrong. Barometer also has 2 different options, "Adjusted for altitude" and not adjusted aka "Station Pressure". Adjust Barometer will always be 29.x inHG, like you see on the weather forecast. Station Pressure (not adjusted) will be lower. Here in Colorado our Barometer will read 24.x. If I use the wrong one I will be way off, even though the rest of my data was correct.

Also if you give me your data I can run it for you and see what we get. If the ballistic data is right/wrong, maybe we can rule that out and look at scope, zero, etc to help you solve what is happening.

Big Thanks!

105g Hybrids. actual length 1.242", G1 .536. Avg. velocity 2985fps, Altitude 950ft. Used 29.92Hg BS.(default). 100 yard zero. Used 1.5" scope Ht. Looks to be closer to 1.75"? Need to get true measurement. Chono numbers where done in 65-70 degree temps. Match was shoot in 45-55 degree temps.

DSCN5687.JPG
 
I ran the data through both JBM and Shooter. Both line up with the numbers your posted. 11.1 MOA give or take. I think you got the calculator correct! Even if I put the incorrect numbers in JBM it only gave me 11.2 MOA.

I would verify your zero, and verify the velocity. If both of those check out, by process of elimination it would be your scope. You could print a "Tall Target" and see if your are really getting the proper adjustment per click. You may also want to shoot at a couple distances to see what your dope is at 300/600/100. That much disparity seems excessive 9% is huge at 600y.

I hope this helps and doesn't just muddy the waters.

Capture.JPG
 
I ran the data through both JBM and Shooter. Both line up with the numbers your posted. 11.1 MOA give or take. I think you got the calculator correct! Even if I put the incorrect numbers in JBM it only gave me 11.2 MOA.

I would verify your zero, and verify the velocity. If both of those check out, by process of elimination it would be your scope. You could print a "Tall Target" and see if your are really getting the proper adjustment per click. You may also want to shoot at a couple distances to see what your dope is at 300/600/100. That much disparity seems excessive 9% is huge at 600y.

I hope this helps and doesn't just muddy the waters.

View attachment 1040212

Will do! Thanks!
 
Will do! Thanks!

I got back to the range to recheck chonograph speed and 100 yard zero. After barrel warn up, I shot the remaining ammo from last week's match.

The good news is the chonograph showed the velocity dead on 2985fps as tested.and used to calculate dial up for 600 yards.

20180310_102134.jpg

Next the scope was dialed back down from the 12.5 MOA dope used in the 600 yard match.
20180310_102541.jpg

With the scope back at zero, I shot the same ammo at 100 yards.

20180310_101138.jpg

The zero was off. It required over 2 MOA to re-zero?? I verified zero just days before the match? I am now confused how it changed/moved? I don't know if the turret was lose and rotated or the scope has an issue tracking up then back down? I guess that's the next focus.

Thanks for everyone's help!!!!!
 
Glad you figured it out! I have no guess on your scope zero. I would watch the guys in your squad, maybe they are sneaky....
 

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