Chronograph or BC Issue?

Katmai

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Hi guys, I took my 300 win to the range today and shot at 700 yards and had some odd results. Either my chronograph is off by 120ish fps or the hornady bc’s on the 220 Eld-x are off, or both. Once I trued my muzzle velocity from 2870 fps down to 2745fps I was golden. With that velocity adjustment, my applied ballistics kestrel changed my elevation from 11.5 moa to 14 moa. I was hitting low at 11.5 moa and when I went to 14 moa I was dead center at 700 yards on an 8” steel plate on every shot thereafter.

My load is 76 grains of h1000, 220 eld x, cci 250 primers and this load is super accurate in my 8 twist custom 300 win mag. Consistently shoots well below half moa at 100 yards with this load.

Anyway, is it common to see such huge inaccuracies with chronographs and/or from incorrect BCs? Going forward, should I true the velocity or the bc?

Thanks,
Ted

 

Katmai

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I forgot to mention my barrel is 23” in case your wondering why my muzzle velocity is lower than many similar loads with a 26” inch tube.
 

Katmai

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Here is the exact data if you’re interested.

exact distance 687 yards
temp 76
barometric pressure 22.63
humidity 28%
altitude 8120 feet

hornady posted bc .329 g7, .645 g1
 

Rjk300

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Hi Jeff,
It’s the old blue Chron.

I have one of those and haven’t used it in many years. It isn’t very accurate I would suggest using a magneto if you have access to one.


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Katmai

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I have one of those and haven’t used it in many years. It isn’t very accurate I would suggest using a magneto if you have access to one.


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Good info. Can I run a magneto if I’m running a suppressor? TB ultra 7.
 

Rjk300

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I don’t run a suppressor so I can’t say with any certainty it will align properly. Hopefully some of the guys with suppressors will chime in.


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OSOK - Crash

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The Magneto (V3 version) comes with heat resistant pads to go under the straps for suppressors.
 

Katmai

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The Magneto (V3 version) comes with heat resistant pads to go under the straps for suppressors.
Thanks, looks like the v3 versions are around $400.

This is likely a stupid question, but is it necessary to have a chronograph if you can validate the drops in the field? Seems like you can back into the velocity if the BCs are accurate?
 

OSOK - Crash

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No. It's not needed. You can validate your drops at distance and true it with your ballistic app. In the Shooter app for example, it's called velocity calibration. You enter your correction needed from your POI to your POA and it will spit out your velocity.

This is how I got my velocities for a couple of years. The chrono is just really nice to have.
 

Katmai

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Ok, that makes sense. If I had a more a accurate chrono I could see how much easier this process would be. In my case, my crappy chrono made the process more complicated than it should be….
 

Broz

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is it necessary to have a chronograph if you can validate the drops in the field? Seems like you can back into the velocity if the BCs are accurate?

The problem doing this is one we often over look. Now if we know for a fact the velocity is the issue, then we can adjust until it matches drops. But if we are not sure and we tweak the wrong input, such as BC when the BC was correct, or velocity when velocity was correct, then we create a situation where the rifle is on that day, in those set of environmental conditions. But then what happens when we go to a different set of conditions on a different day? Most likely we will be off again. So if at all possible, whenever we can, we need solid accurate data.
 

Katmai

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The problem doing this is one we often over look. Now if we know for a fact the velocity is the issue, then we can adjust until it matches drops. But if we are not sure and we tweak the wrong input, such as BC when the BC was correct, or velocity when velocity was correct, then we create a situation where the rifle is on that day, in those set of environmental conditions. But then what happens when we go to a different set of conditions on a different day? Most likely we will be off again. So if at all possible, whenever we can, we need solid accurate data.
That makes a hell of a lot of sense and I can see an endless game of chasing your tail as environmentals change. Sounds like I should invest in a good chronograph to insure I’m getting accurate velocity to start with, Then tweak BCs as needed. Thanks for the useful tips.
 

FURMAN

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As stated above those style chronographs are very unreliable. To add to it Hornadys listed bcs are not accurate. I’ve had the best luck using the middle of their stepped bcs but the calculator may still need to be adjusted. In this case you really do need an accurate velocity or you’ll be chasing your tail as others have said.
 

OSOK - Crash

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@Broz and @FURMAN, that is for chiming in here. I learned something new. My question is... When do you know which variable to adjust? BC or velocity?


Sorry to OP for giving bad info above. It was not my intention. That method has worked for me in my environment of flat Midwestern hunting, and 700 max range.
 

Broz

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Well if you have enough velocity data from a trusted chronograph (Magneto Speed or Lab Radar) You should be good on velocity. What I do is toss out any that are off as in the lowest or the highest and then average the rest. I am talking ones that look to be errors as they are so far off. Then you can trust your velocities you have left. After that, check zero first if things don't line up. If you shoot off a bench all the time, check zero off the bench. If you shoot prone, then check zero prone. Also make sure you are properly adjusting out all parallax movement when zeroing. From there, you can be confident it is likely the BC. But I rarely need to adjust it using Bergers advertised BC's. There are companies that exaggerate their BC's or get them in a way to give a false number. I won't name names, but there is one solid copper offering out there that is so far off it is almost laughable.

Remember, if a rifle shoots 1/2 moa low or high at 300, 500, 700 and 1000. It is likely the zero that is off by the 1/2 moa. What you are off on the zero, will be the same all the way out.
 

Broz

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@Broz, which do you adjust when you don't have a chrono. Or a trusted one, as the OP situation has.
Take your pic. it falls back on the old long range solver saying. "Garbage in Garbage out" If you want to be as good as you can be, you must have solid data. If not it is just a guessing game.
 

Katmai

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Take your pic. it falls back on the old long range solver saying. "Garbage in Garbage out" If you want to be as good as you can be, you must have solid data. If not it is just a guessing game.
Sounds like I need to spend $400 on a magneto Chrono😀. From what I’ve read on this site, it sounds like I should lab radar?
 

Katmai

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I meant to say, it sounds like I should avoid lab radar? Sounds like folks on this site have had issues with reliability and customer support?
 

Katmai

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Scheels had one magnetoSpeed v3 in stock and I just bought it. I will pick it up today and try to verify velocity this weekend. No need to answer my lad radar question. I will update you this weekend with actual results in case you’re curious what the actual velocity is. Should be interesting to see if it’s a bc or velocity issue.
 

Katmai

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And thanks for the great info, you guys saved me a lot brain damage trying to figure this out!
 

Broz

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Scheels had one magnetoSpeed v3 in stock and I just bought it. I will pick it up today and try to verify velocity this weekend. No need to answer my lad radar question. I will update you this weekend with actual results in case you’re curious what the actual velocity is. Should be interesting to see if it’s a bc or velocity issue.
I have one and it never misses. It is important to know you should leave it off during load development and use it after to get solid velocity data. The reason is it will effect the harmonics of the barrel and also point of impact. But it is a great tool and they are accurate. I have both and have ran them together to measure the same bullets velocity. They are rarely more than a few fps apart.

For the record, AB has the .308 Hornady 220 gr ELD X with a G7 BC of .333 I would use that to start
 

Katmai

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I have one and it never misses. It is important to know you should leave it off during load development and use it after to get solid velocity data. The reason is it will effect the harmonics of the barrel and also point of impact. But it is a great tool and they are accurate. I have both and have ran them together to measure the same bullets velocity. They are rarely more than a few fps apart.

For the record, AB has the .308 Hornady 220 gr ELD X with a G7 BC of .333 I would use that to start
Thanks for the info. Good point, I will only use it to capture velocity as I can see how that additional weight would impact accuracy and point of impact.

As for the BC, will try that. This is what they show on the Hornady sight.
C928182A-518C-4132-A339-398679C29861.png

 

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