Drop/MV discrepancy

[mmw194287]

At the risk of sounding completely ignorant, I'm scratching my head over this one so I thought I'd see if anyone has any thoughts....

I started shooting the ABM 215 Berger Hybrids out of my 300 Win Mag (28" barrel) and have been happy with the accuracy, groups, etc. I zeroed at 100yds, shot good groups on paper at 300, and then took it out to shoot some steel, rocks, etc. At longer ranges it was shooting much higher than my calculator was predicting (I had to click down 3 or so MOA to hit a target at 600 after ranging it). So I decided to shoot at a single target at 100 yard intervals out to 500 to see exactly how it's dropping.

I'm getting MV readings right around 3000 fps (2992, 2995, 2985, 2997, 3010, etc.), but in order to get a calculator to match my actual drop at 500yds I need to input a MV of roughly 3300 fps. At 500, it's dropping only 28.5 inches or so and grouping very well (see photo, left side of tape is plumb with the bullseye), but when I plug in my environmentals and the MV I'm getting from the chrono it tells me I should be seeing a 38.5" drop. Pretty significant difference.



I know that ballistic calculators need to be verified with real world dope, but I'm pretty shocked at the discrepancy I'm seeing. In my past experience, running a factory load through a calculator it usually pretty accurate with some fine tuning. But 10 inches higher than expected at 500 yards? And I've run it through a bunch of different apps/websites: Shooter, JBM, Berger, etc.

Is there something I'm missing? Anyone else had any similar experiences? As far as continuing to verify my drop, if I'm matching the much faster 3300 fps profile, should I continue to work from those estimates?

 

[Minnesotamulisha]

I would say the BC you put into the ballistics calculator isn't correct. Depending on your app, you can modify it to match actual experiences.

I use Strelok and I can adjust it that way. Give me a minute and I can screen shot it.

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[Minnesotamulisha]

Heres what it looks like. I can enter muzzle velocity and yardsge and determine the BC. The longer the range, the better.

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[mmw194287]

I would say the BC you put into the ballistics calculator isn't correct. Depending on your app, you can modify it to match actual experiences.

I use Strelok and I can adjust it that way. Give me a minute and I can screen shot it.

Sent from my SM-N920V using Tapatalk

Thanks for the reply. I'll have to check that out, as BC is the only number I haven't thought to recheck (mainly because I'm loading that data straight from the factory profile from Berger).

 

[luke moffat]

You got the correct sight sight inputted? Using correct DA or pressure and temp (not that it would make that big of diff at 500). Using the .696 with the G1 setting not using .696 with G7. Is your zero a true 100 yard zero right on the money? Any or a couple of those things could account for it. But a 300 fps velocity increase likely isn't the cause. Maybe the scope isn't tracking?

 

[LaHunter]

Luke brings up a good point about the scope tracking true. Some scopes may list the clicks as 1/4 moa, but in reality it is not always the case. What scope are you using?

 

[Rckymtnshooter]

According to applied ballistics the most common error with a ballistic app is the actual value per click of adjustment for your scope. I had the same issue you are having.
Look up the Litz tall target test. Run though this test and determine if you have a correction value for the number off clicks and actual distance moved. This solved my issue as my scope was actually moving the impact 95% of what it should have been. The applied app has a section where you can enter this correction. After running though this test and enter that new value my app is right on the money.

 

[mmw194287]

Luke brings up a good point about the scope tracking true. Some scopes may list the clicks as 1/4 moa, but in reality it is not always the case. What scope are you using?

It's a Nightforce SHV 5-20.

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[ckleeves]

Your 100 yard zero is absolutely perfect? If your input is perfect then the output is perfect on ballistic calculators you just have to figure out that perfect input which is sometimes the tricky part!

 

[mmw194287]

Thanks for all of the input and thoughts--much appreciated. To the best of my ability to shoot/judge, the 100 yd. zero is on. Even still, if I change the input on the ballistic calculator so that it shoots 1", 1.25", 1.5", 2" etc. high @ 100, it still doesn't match the real world drops I'm getting out to 500.

I don't think the issue I'm encountering is the scope clicks, as when I was shooting today I maintained the same point of aim on the same target (without adjusting elevation) moving it out 100 yard at a time. I shot good groups--the 500 yard group was sub 1/2 MOA and an inch off plumb from the point of aim. What's throwing me for a loop is just that the it just seems to be shooting way flatter than everything tells me they should.

It just seems odd that I can't produce a ballistic profile that matches what the rifle/load does on target without reverse engineering some of the numbers. When I run my chrono'd MV and and 500 yard drop into Strelok to calculate a new BC (per Minnesotamulisha's advice), it does allow me to reproduce each of my measured drops accurately, but the BC it produces is wildly different than what Berger lists.

In any event I'm going to go back to the range and reconvince myself that the zero at 100 is absolutely perfect, and then I'll likely check the profile produced with the reverse engineered B/C out at 100 yard intervals out beyond 500. I'll have to look into the Litz tall target test too.

Thanks again for the help. Feel like I'm overthinking things and overlooking things at the same time.

 

[doverpack12]

Make sure you are inputting the correct pressure either station or absolute. Also AB had a glitch earlier this year and best way to get rid of it was to sync the profile to compute delete the app then reinstall the app. Tall target test could tell you a lot also.

 

[mt100gr.]

It's a Nightforce SHV 5-20.

Sent from my SM-G930V using Tapatalk

Interesting....I am having a similar issue with a 300 win mag shooting 215s from a 28" barrel. Same scope too.

My impacts are low.

I am more in the ~150 fps discrepancy range to get the profiles to match but I don't think I am buying it. I use AB and have been playing with the scope click value and tweaking that to see if thing line up.

Interestingly, strelok pro gives me almost perfect drops for the load.

I would like to know more about the AB glitch from.earlier.this year if anyone has any info although AB is rocking with my 7mm drops with a minor velocity correction.

 

[luke moffat]

I don't think the issue I'm encountering is the scope clicks, as when I was shooting today I maintained the same point of aim on the same target (without adjusting elevation) moving it out 100 yard at a time. I shot good groups--the 500 yard group was sub 1/2 MOA and an inch off plumb from the point of aim. What's throwing me for a loop is just that the it just seems to be shooting way flatter than everything tells me they should.

When someone says the scope isn't tracking they aren't reffering to it not holding zero or able to shoot great groups which it sounds like yours is doing great at that which is good.

Tracking means that 1/4 MOA adjustments you input on the scope isn't actually 1/4 MOA and thus making you end up 2 MOA off of elevation at 500 yard which is A LOT in my opinion.

How I read it above you weren't using the turrets as you kept moving out but rather were using the reticle for hold over as you said you weren't adjusting the elevation? Are you sure you were using the right hold over hash mark on the reticle....might explain why you were exactly 2 MOA high?

Def something going on though. I would be surprised if your SHV isn't tracking.....likely some other input in the program. How many MOA did Strelok tell you to dial/hold with 2995 fps average, 29.92 pressure, and 60 degrees with that 215 and .696 BC for 500 yards?

 

[doverpack12]

Unless you are pretty much at sea level 29.92 is the wrong pressure to be using for your drops. Make sure the toggle switch is off for Absolute Pressure and input something less than sea level/corrected station pressure reported by the weatherman. There are some handy free apps that will do this on your phone and give you a close elevation as well.

 

[mmw194287]

When someone says the scope isn't tracking they aren't reffering to it not holding zero or able to shoot great groups which it sounds like yours is doing great at that which is good.

Tracking means that 1/4 MOA adjustments you input on the scope isn't actually 1/4 MOA and thus making you end up 2 MOA off of elevation at 500 yard which is A LOT in my opinion.

How I read it above you weren't using the turrets as you kept moving out but rather were using the reticle for hold over as you said you weren't adjusting the elevation? Are you sure you were using the right hold over hash mark on the reticle....might explain why you were exactly 2 MOA high?

Def something going on though. I would be surprised if your SHV isn't tracking.....likely some other input in the program. How many MOA did Strelok tell you to dial/hold with 2995 fps average, 29.92 pressure, and 60 degrees with that 215 and .696 BC for 500 yards?

Sorry I didn't explain it better. After noticing the inconsistency when trying to dial using the numbers from the app, I took a 6 foot piece of plywood, put a bullseye on top, and shot at my 100yd intervals, each time holding the crosshairs on the same bullseye. No adjustments, no holdover, etc., just wanted to get a sense for the actual flight path of the bullet (i.e. to see if I hold "on" at 500, how much lower is the actual impact). I ended up with five groups strung along the vertical axis, and measured down from the bullseye to see how the bullet it actually dropping from my zero. Checking those numbers against the app numbers is what has me puzzled.

Strelok (and every other app I've tried) is telling me to dial/hold 7.4 MOA/39 inches of drop with that data. But when I hold on with my 100 yard zero, I'm grouping at 28.5 inches low @ 500.

 

[luke moffat]

Sorry I didn't explain it better. After noticing the inconsistency when trying to dial using the numbers from the app, I took a 6 foot piece of plywood, put a bullseye on top, and shot at my 100yd intervals, each time holding the crosshairs on the same bullseye. No adjustments, no holdover, etc., just wanted to get a sense for the actual flight path of the bullet (i.e. to see if I hold "on" at 500, how much lower is the actual impact). I ended up with five groups strung along the vertical axis, and measured down from the bullseye to see how the bullet it actually dropping from my zero. Checking those numbers against the app numbers is what has me puzzled.

Strelok (and every other app I've tried) is telling me to dial/hold 7.4 MOA/39 inches of drop with that data. But when I hold on with my 100 yard zero, I'm grouping at 28.5 inches low @ 500.

How low were your shots at 200, 300 and 400?

 

[mmw194287]

How low were your shots at 200, 300 and 400?

2.25" @ 200, 8" @ 300, 16" @ 400. A lot flatter than anything else I've shot from my .300--to the point that it doesn't make sense to me.

Thanks for your thoughts, Luke.

 

[luke moffat]

Maybe your rangefinder is buggered

 

[mmw194287]

Maybe your rangefinder is buggered

At this point, I'm willing to consider any possibility!

 

[pods8 (Rugged Stitching)]

If you are not already using Ballistics Calculator | Applied Ballistics, LLC I highly recommend it for tuning in your dope. The cheap calculators are fine for shorter stuff but the errors start really stacking up as you stretch. Litz's calculator takes some time to get everything input and refined to match what you are really seeing but when you get there it falls into place.

Temp, air pressure, humidity, scope centerline over bore, velocity, use his BC's (which are lower than the manufacturers), etc and you'll get it dialed in. I had originally developed a dope chart from a 200yd zero and 400yd verification target but found it was off when pushed to ~700yd. When I when back through I found little errors at 200 and 400 that extrapolated to be incorrect further out, 1/4" type stuff.