Thread: Ballistic truing conundrum

Originally Posted by 11mms

What's the objective in asking?
To me I'd call this "dope" and get on with my day... but i spose if you want to dial in a computer thingy then yeah... you need to work out the whyfor.

I want to understand “the why”. That’s the way my brain works & as @andyanimal31 says confidence in data is critical. Last thing you need is the double guessing yourself.

If the dope came in low, ie need to dial up a few clicks I can understand that & have seen it plenty of times before.
But to be 10% out the other way is a massive outlier and something I need to get to bottom of.

I'd be inclinded to try truing it at a few different ranges, say 350y and 500y.
That will tell you if your velcoity is right or not.

Unless the atmposherics are messed up in your ballistic calculator (seems unlikely that both would be out), it's either;
-Bad zero (It'll be easy to see if your zero was off 1 moa, 2"@ 200yards)
-Your scope
-Your chrony (if the 284 was ok then rule that out)
-Funky stuff happening with wind down range (if you didn't notice the same issue with the 284 then rule that out too).

The scope might not be dialing correctly (Gimp had a video a few years back of a Mark 6 that dialed on the piss). You can test this by doing a box test, or just a simple elevation test. I had a VX5 that didn't dial right, the clicks were quite calibrated/manufactured correctly.
If you can easily pull the scope off and put it on a 22 then you can do a full "tall target" tracking test without wasting 30 rounds of 7SAUM ammo.

Have you validated the BC of the bullets is correct to what you are using? Sometimes the advertised figures aren't right and the error you get can be surprising. I didn't see that mentioned anywhere above? It might not explain all of the error you are experiencing but there may be several smaller errors adding up. Have you tried a different chrony as well?

Originally Posted by No.3

Have you validated the BC of the bullets is correct to what you are using? Sometimes the advertised figures aren't right and the error you get can be surprising. I didn't see that mentioned anywhere above? It might not explain all of the error you are experiencing but there may be several smaller errors adding up. Have you tried a different chrony as well?

I thought this too, just forgot to added it to my post...
That would also show up by validating at more distances.

Hornady list the BC for the bullet in velocity bands, if you have a multi BC function on your calculator then use that, otherwise using their middle number is generally more accurate.
The G1/G7 BC for the 162 ELD-M is 0.655 / 0.329.

https://www.hornady.com/support/ballistic-coefficient

Originally Posted by No.3

Have you validated the BC of the bullets is correct to what you are using? Sometimes the advertised figures aren't right and the error you get can be surprising. I didn't see that mentioned anywhere above? It might not explain all of the error you are experiencing but there may be several smaller errors adding up. Have you tried a different chrony as well?

It sounds like he is using a kestrel 5700.
If that's the case they have applied ballistics custom drag curves.
They aren't wrong end of story.
To me, the culprit is the 1.3 high at 100 for a 200 yero
Actually zero at 100 and try your data out from that.
I have seen most things in my time.
Just had one the other day with the guy having problems.
Have you zeroed?
Yep, shows me a tiny 3 shot group through the dot.
I went and validated and it was coming up at a lower speed than I though it should be.
Rang me to say way low at 350.
Fucked if I know,recheck the zero.
Guess what, zero out, fixed that and bang on out to a km and back


Sent from my SM-A226B using Tapatalk

Thanks all for the comments and feedback. To pick up on a couple of points above :

BC - i used 0.67 G1 as listed by Hornady. If anything manufacturers stated BCs tend to be “optimistic” and derived under ideal conditions. In my case if a lower BC were correct this would not explain the data I’m getting. Dialing 9.0 moa compared to ballistic program 10.12 moa. A lower BC would require a bigger come up, not smaller. Or conversely the BC would need to be up around 0.7 or something to make the numbers line up.

Chrony error, using a Magneto Speed. Have used on many other rifles previously and not observed it to be inaccurate previously. Every measuring device has a degree of precision or error, so possibly 1-2% out ? But to get the observed come up difference of 9 vs 10 moa requires a muzzle velocity of ~3100 fps compared to my measured 2995. Just can’t see 3100fps being possible with a 22in bbl SAUM. Wouldn’t it be nice though !!

Scope dial up calibration - did that today with tall target at 100.0 yards measured at the erector. Surprisingly the VX6 is dialing better than moa !!
First time I’ve seen this in a Leupy or any scope for that matter. This one is dialing 1.083in per moa, instead of 1.05in/moa. That translates to a 3% error. So dialing 9.0 moa is actually giving a come up around 9.2 moa.
So this still leaves 0.75 - 0.8 moa “unexplained”.
Or my muzzle velocity is something like 3075fps ?

At this point my guess is I’m dealing with several compounding errors.
1. Scope dial up
2. Zero maybe slightly out, should be able to verify this next weekend at NZDA range if weather plays ball.
3. Chrony might be reading slightly low

I agree @Beetroot, running checks at 300 &/or 500 yards would be wise and helpful.

When I replaced my mark 4 with a vx 6 I had the same issue as you but using 162 amaxs in a rem mag. Thought it was the scope adjustment as has been mentioned above (around 1.08in/moa) so just fudged the speed (increase of about 75fps) to match. A while later when I tried a different load in the rifle using 180eldms I just assumed it would be the same with the scope over adjusting, but was surprised when it came to checking at distance is was actually back to around 1.05in/moa. Still have no idea why but it's consistent so havnt worried.

Originally Posted by chainsaw

Thanks all for the comments and feedback. To pick up on a couple of points above :

BC - i used 0.67 G1 as listed by Hornady. If anything manufacturers stated BCs tend to be “optimistic” and derived under ideal conditions. In my case if a lower BC were correct this would not explain the data I’m getting. Dialing 9.0 moa compared to ballistic program 10.12 moa. A lower BC would require a bigger come up, not smaller. Or conversely the BC would need to be up around 0.7 or something to make the numbers line up.

Chrony error, using a Magneto Speed. Have used on many other rifles previously and not observed it to be inaccurate previously. Every measuring device has a degree of precision or error, so possibly 1-2% out ? But to get the observed come up difference of 9 vs 10 moa requires a muzzle velocity of ~3100 fps compared to my measured 2995. Just can’t see 3100fps being possible with a 22in bbl SAUM. Wouldn’t it be nice though !!

Scope dial up calibration - did that today with tall target at 100.0 yards measured at the erector. Surprisingly the VX6 is dialing better than moa !!
First time I’ve seen this in a Leupy or any scope for that matter. This one is dialing 1.083in per moa, instead of 1.05in/moa. That translates to a 3% error. So dialing 9.0 moa is actually giving a come up around 9.2 moa.
So this still leaves 0.75 - 0.8 moa “unexplained”.
Or my muzzle velocity is something like 3075fps ?

At this point my guess is I’m dealing with several compounding errors.
1. Scope dial up
2. Zero maybe slightly out, should be able to verify this next weekend at NZDA range if weather plays ball.
3. Chrony might be reading slightly low

I agree @Beetroot, running checks at 300 &/or 500 yards would be wise and helpful.

If you are using the kestrel use the bc data on the kestrel phone app.
A g1 bc for the saum will not be correct.
Either use the kestrel g7 or custom drag curves it comes with.

Sent from my SM-A226B using Tapatalk

Pretty sure the Hornady guys recommend adjusting velocity, not BC, for 'truing'.

Originally Posted by caberslash

Pretty sure the Hornady guys recommend adjusting velocity, not BC, for 'truing'.

As a rule it is best practice.
If you have a brian litz bc/applied ballistics/kestrel use their custom drag curves.
It's all sorted with out mucking around with velocity bands.
If you have all the right info your chrony speeds will be very close to real world results.
Don't fuck with the Bc's

Sent from my SM-A226B using Tapatalk

Originally Posted by chainsaw

At this point my guess is I’m dealing with several compounding errors.

This. Accuracy is minimising all of the errors you can so that the ones you can't have a smaller effect (eg meteorological factors).

https://www.nzhuntingandshooting.co....et-test-35034/
https://www.nzhuntingandshooting.co....34/index3.html Post #40

Range finding error ?
625 is a random number, so I guess the target is at a convenient spot with a rising bank behind the target and perhaps some rounding of the distance to the nearest quarter-hundred ?
Its tricky to get an exact measurement on flat or rolling ground and a laser might not register off a small target frame like a gong. It could be confirmed by parking a vehicle at the firing point and ranging back to it while standing at the target.
For my 7mm08 the difference in drop from 625 yd back to 600yd is almost 1 moa.

It’s an accurate 625yd, measured with 2 different RFs and one i have used multiple times over the years. I range it every time & get the same distance. And never before with various different calibres, rifles, scopes have I encountered the situation where I need LESS dial up by a factor of 10%. In other cases the dial up predicted by ballistic programs is very close to correct or slightly low, ie need to come up 1 or 2 clx.

Originally Posted by chainsaw

It’s an accurate 625yd, measured with 2 different RFs and one i have used multiple times over the years. I range it every time & get the same distance. And never before with various different calibres, rifles, scopes have I encountered the situation where I need LESS dial up by a factor of 10%. In other cases the dial up predicted by ballistic programs is very close to correct or slightly low, ie need to come up 1 or 2 clx.

If this is a target you have shot multiple times with no issues, your chrony has proven to be reliable in the past, and on the same day you shot another rifle that performed as expected (so no funny wind conditions) then you can work out what variables you can discount and which ones to focus on.