Big discrepancy between chrono MV and real world shooting. Why?

[willfrye027]

I don't want to derail, but I have a related question.

How many of you don't use a chrono at all?

I don't own one. I zero at 100 yards. Take the velocity of the box, minus 30 fps per inch if the barrel is less than 24 inches. Put that into the calculator (Shooter) to get "try" dope. Shoot at 300 and 500 yards. (my range only goes to 500). Tell the calculator what my actual drops are and let it figure out what it thinks my MV is. Anyone see an issue with this process?

Not an issue at all. Works better if you can shoot a lot farther. I’ve got a magneto speed which just makes it a little easier but I still have to validate at distance and sometimes adjust but 20fps or so to get things lined up perfectly

 

[PineBrook413]

As long as ll your data is good....known velocity from chrono (10 shot avg), twist rate, scope over bore, exact zero at known yardage etc. All you need to "true" up with your ballistic chart is BC.

If you start changing velocity your giving your ballistic calculator bad info. You have a known velocity, keep it.

BC from manufacturer isn't always honest. Also the BC isn't the same at all velocities so you need to input the correct velocity and then adjust the BC in my opinion.

Obviously all that you really needed is a precise zero, environmental data, height over bore, twist etc and then go out and collect DOPE so you have known data on target at multiple ranges. We always confirm 100 yard zero and then shoot 200, 400, 600, 800 and record all data in a log book. Do that 3-4 times at varying times before hunting and you'll have a pretty rock solid chart.

 

[EdP]

The recommendation to adjust BC strikes me wrong in this situation. The OP would have to adjust his BC UP because his strikes are higher than predicted. I think it is pretty well accepted that mfgs published BCs tend to be overstated vs under. Have you long range guys found BCs under predicted?

 

[Formidilosus]

The recommendation to adjust BC strikes me wrong in this situation. The OP would have to adjust his BC UP because his strikes are higher than predicted. I think it is pretty well accepted that mfgs published BCs tend to be overstated vs under. Have you long range guys found BCs under predicted?

No. Adjusting BC is the exact wrong answer.

 

[mxgsfmdpx]

OP, have you gone back out and eliminated your errors? Any luck getting on at 100 instead of "1/2 high" at your sight in range? Have you tried a "second opinion" on your chronographing? I've found as high as 100 FPS discrepancies between two "qualified" chronographs with hand loads.

 

[Hoosker Doo]

OP, have you gone back out and eliminated your errors? Any luck getting on at 100 instead of "1/2 high" at your sight in range? Have you tried a "second opinion" on your chronographing? I've found as high as 100 FPS discrepancies between two "qualified" chronographs with hand loads.

No further progress yet. I'm in the process of reloading some more because I was starting to run low on rounds, and I read the vasectomy thread on here too much, so I'm out of commission for a couple days haha.
I'll get a true 100 yard zero, and see if I can get ahold of another chronograph, but it might take a week or so.
I appreciate the wealth of knowledge and advice being shared. Thanks all!

 

[Justin Crossley]

DO NOT ADJUST BC based on shooting at 500 yards.

 

[SDHNTR]

DO NOT ADJUST BC based on shooting at 500 yards.

Agreed, but I thought he was shooting at 800+ yards?

 

[Macintosh]

I thought normally bc truing was supposed to be done approaching transsonic?

 

[Hoosker Doo]

Agreed, but I thought he was shooting at 800+ yards?

I shot at that range for fun, but am working to get everything tuned in out to 600 before hunting season, and then keep shots under 500 on game. Maybe post season, I can work on extending my range after I work out all the bugs.

My money is on input error(s), and likely some shooter error sprinkled in. Most often, these issues are several smaller errors that compound.

I input the following in Revic:

Sight in range = 100 yards (per OP)
Zero elevation offset = 0.5” (per OP)
Zero windage offset = 0.0” (unknown)
Ammo MV = 3033 fps (per OP)
Scope height = 1.75” (per OP)
Bullet BC/Doppler file = per Revic app
Elevation = 7000’ (Per OP)
Temp = 55* (per OP)
humidity = 50% (unknown but doesn’t matter much)

422 yard prediction is 4.9 MOA.


812 yard try dope is 14.7 MOA.


Anyways, I hope the OP gets it figured out after his junk is healed up.

Wow. Your Revic data was halfway between what Hornady and AE ballistics came up with and what my "actual" data was. And your inputs look consistent with mine, but I will double check see why they are so different.

It's not hard to see how a slightly off 100 yard sight in and a possible incorrect MV could turn a 4.5 MOA adjustment to 4.9 MOA vs 5.5 moa that Hornady told me. After I true things up and collect some more data, maybe I'll look into Revic as well.

 

[SDHNTR]

I shot at that range for fun, but am working to get everything tuned in out to 600 before hunting season, and then keep shots under 500 on game. Maybe post season, I can work on extending my range after I work out all the bugs.


Wow. Your Revic data was halfway between what Hornady and AE ballistics came up with and what my "actual" data was. And your inputs look consistent with mine, but I will double check see why they are so different.

It's not hard to see how a slightly off 100 yard sight in and a possible incorrect MV could turn a 4.5 MOA adjustment to 4.9 MOA vs 5.5 moa that Hornady told me. After I true things up and collect some more data, maybe I'll look into Revic as well.

Ok, I read your original post as trying to true drops at 8 something. I think that’s what you said. BC starts to matter at that range. I agree with the other guys at 500 or less it’s certainly not your problem.

 

[SDHNTR]

Let it go man, adjusting BC at 812 yards in this circumstance is a JV move.

That’s your opinion. I agree that proper zero and accurate Mv is far more important, but Im also not disregarding BC at that range.

 

[SDHNTR]

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Lulz, dem wascally ammo mfg underreporting BCs by 25%

Of course they do. I never said otherwise. I’m not sure what point you’re trying to make.

 

[Formidilosus]

Of course they do. I never said otherwise. I’m not sure what point you’re trying to make.

I believe he’s trying to point out that it takes a massive change in BC to even move a couple of inches at 800 yards- way larger than is ever happening due to individual barrel differences. Very, very people could remotely shoot the level required to nail down an error of less than an inch at 800 yards due to a BC change. Hornady Doppler, Applied Ballistics, etc are giving very solid BC numbers these days and that is not what causes errors.

 

[huntnful]

I'd fix the zero and true the MV to hit center at 800 yards. And just accept that I'm slightly high at closer yardages. I don't think I've ever had a calculation of BC & MV hit dead center at every yardage from 300-1200 yards. Seems like it might be a touch low at one yardage or a touch high at another yardage. So I personally just true at the furthest yardage, and then verify that the closer yardages still land well within a vital circle, and roll with it.

 

[bmart2622]

Of course they do. I never said otherwise. I’m not sure what point you’re trying to make.

Hes saying youre wrong....again

 

[SDHNTR]

I believe he’s trying to point out that it takes a massive change in BC to even move a couple of inches at 800 yards- way larger than is ever happening due to individual barrel differences. Very, very people could remotely shoot the level required to nail down an error of less than an inch at 800 yards due to a BC change. Hornady Doppler, Applied Ballistics, etc are giving very solid BC numbers these days and that is not what causes errors.

I figured. So then what’s “massive”? And I agree those sources probably aren’t going to steer you wrong, but the box sure can. Enough to matter to the point that I’m gonna do what I can to not take it at face value get it as accurate as I am able. Because why not?

This is silly. We’re arguing over stupid stuff, and are mostly in agreement even. My only point is, if we are truing stuff, why not make an effort to be as accurate as possible with both?

 

[bmart2622]

Mostly in agreement!!! Thats true, but everyone but you agrees to NOT adjust BC!!!

 

[SDHNTR]

Mostly in agreement!!! Thats true, but everyone but you agrees to NOT adjust BC!!!

My goodness, my point got taken out of context. I’m done with this thread.

 

[Formidilosus]

I figured. So then what’s “massive”?

30 point difference in G1 BC. For the bullet being discussed (162gr ELD-X) 2 inches at 800 yards is 30 points. From a .630 to a .600- that isn’t real. I’ve seen a bunch of guns shot over Doppler and Oehler 88’s and there is maybe a 5-10 point difference between guns.

And I agree those sources probably aren’t going to steer you wrong, but the box sure can. Enough to matter to the point that I’m gonna do what I can to not take it at face value get it as accurate as I am able. Because why not?

Because unless you have a Doppler or Oehler 88, you can’t see the difference. So you aren’t “correcting” anything, you are just covering up what is really causing the error.

That’s for bullets that have actually been measured- most have at this point. The ones that haven’t are either boutique and need to be measured, or are from companies trying to fake it.

This is silly. We’re arguing over stupid stuff, and are mostly in agreement even. My only point is, if we are truing stuff, why not make an effort to be as accurate as possible with both?

Well, I get multiple messages a month referencing trying to fix someone’s elevation discrepancy by trueing BC. It’s never the answer. I’m not trying to be rude- almost no one should be trueing BC until very long ranges, much further than nearly anyone is shooting animals. I will go a step farther and say that almost no one regardless of what they are doing should be trying to true legit BC’s by drops. You just can’t see the difference between a .631 and a .624 G1 BC (real numbers from the OP’s bullet).