Ok, I have been shooting and reloading for a while, I have a chrono, I understand the concept of Ballistic coefficients, and I know who Brian Litz is.  I have good gear, good glass, good technique and can hold reasonably tight groups at distance.  

My problem is the math never works.  I chrono my loads out of the actual gun, then look up the BC from the manufactures.  
I plug my verified numbers into any ballistic calculator you care to name, and it tells me should have XX" of drop at a given range or that the "3rd hash mark on my scope reticle" (or whatever) should correspond with XXX yards and it's NEVER right.  My group is OK, but the elevation past 100 is never right.  

So, I have invested in a couple of scopes with better reticles and more precise adjustments, and tried to use factory ammo as a control.  I chrono my loads out of the actual gun, because factory ammo velocity figures are a joke.  I plug the numbers into the scope manufacturer's calc and the ammo manufacturer's calc, and get different numbers, neither of which seem to correspond with the live fire results I obtain.  It's utterly ridiculous.  

I even tried using .22LR, with actual chronoed velocities from that gun, and then testing the numbers only to find a 10" difference in the predicted drop at 200 and the actual group.  In this example I was able to hold just over a 2 MOA group at 200 yards with federal AM22 with barney rounds out of a green mountain 10/22.  In case anyone cares, a 10/22 barney round is chambering a round, then inserting a 10 round mag, and firing the first round into the dirt, then recording the full 10 round group avoiding the 1st round flier.  

Now, I know every one of these calcs has warnings and disclaimers out the wazoo about being only guesstimates, but seriously, there has to be a way to predict that at xxxx velocity a bullet with .xxx BC should drop xx" and have it be at least close to reality.  At the moment I cannot trust a cold bore shot at anything more than about 100 unless I have previously zeroed at that distance (hard to do when my local range only has 100Y)

At this point I HOPE there is something stupid that I am overlooking.  

Just in case anybody is wondering the reason this is important to me is that occasionally find myself in the position of having to go to a match with more than one type of ammo, for example we have a local 200-yard high-power match. Recently because I decided to go to the match at the last minute I was stuck bringing two different types of ammo. I brought perfecta 308 and PMC bronze 308. Previous experience has taught me that the perfecta is a lighter load than the PMC bronze, and neither one are Target ammo but for 200 yards they should have been good enough.
When I had chrono with them previously the PMC was a good two hundred feet per second faster than the perfecta, but at 200 yards where I should have had to adjust by a couple of MOA, their POI were the same.

give us an example to work with.   pick a centerfire with a good bullet, not rimfire

what rifle, scope, cartridge, bullet, etc?
what are the measurements?  e.g. height over bore of scope, twist, etc

what chrono are you using and what mv do you get?  measure at least 10 rounds and list the individual shot values

what were the atmospherics? DA, temp, whatever


what is your actual measured drop at two distances past 400 yards?
what do you think it should be based on the calc?

Are you shooting on level ground, or up/down elevation?  Do your calculators take the height over bore of your optic into account?

No calculation out of the box has ever been perfect for me either, but I can with regularity come up with a new load, dial in the known variables from my zero (BC and velocity), and get onto say, a 20" diameter plate at 600 yards. 

Have you verified the scopes turret adjustment at 100 yards by shooting a group and then dialing 20 moa up and measuring to make sure your scope is tracking the right amount? One of my scopes tracks 0.3 instead of 0.25. That and an incorrect scope height could be given an error.  Another thing that causes some problems is to accidentally turn the powder temperature setting on and have a error that way. With out actually watching you it's hard to diagnose what is going on.

I kinda think this is unlikely but where are you hitting at 25 and 50 yards with a 100 yard zero. If you have to high a scope mount and your bullet is zero at 100 but low at 50 and not crossing your line of sight it could be higher given false readings.

If the math doesn't work then your inputs are wrong. Plain and simple. If you want help understanding the proper way to identify your inputs you can email me at ballisticxlr at gmail and I'll help you out. This is an extremely common condition, you've got the knowledge of the how but knowing exactly which what is which is important. I'll work you up a ballistics table and I'll betcha a dollar by paypal that it works if you do your part.

I agree with the above.

Last week, I zeroed a new scope at 100 yards and chrono'd ammo on a Magnetospeed.  Gorgeous weather, sunny, minimal wind, 77*, about 30% humidity according to the Kestrel.

Yesterday, I took the same gun and same lot of ammo (factory Hornady 140gr ELD-M) and shot at 600 yards.  It was about 55*, very foggy, very humid, with a slight mist in the air, and some wind.

The Hornady 4DOF app on my phone called for 4.89 mils of elevation at 600 yards with my 100 yard zero.  I ended up dialing in 5 mils even (50 clicks on my scope versus the ~49 called for).  

Given the changes in weather conditions and the fact I had never shot at 600 yards before, I'd say the ballistic calculator was pretty much on the money.

ETA: POI at 600 yards with Hornady 140gr BTHP was WAYYY different than the 140gr ELD-M.  "Duh" to people with experience, but it was a surprise to me.  Almost .9 mils lower.

.9 (point 9)

Typo fixed.  

Ok, I am probably doing this wrong, so here goes, with Real World data.  I am shooting within a couple of degrees of level both during zero and at the matches.  


First I fire up Vortex's LRBC (not to pick on them, but they conveniently have my factory ammo programmed)


My Chrono data:

Day of zero:
Factory PMC 147 Bronze .308
2686
2734
2713
2733
2766

av 2726.4
SD 26.38636011

Previous outing:
Factory PMC 147 Bronze .308
2749
2703
2763
2714
2739


AV 2733.6
SD 22.141364


I only had 100 yard range to zero, so I zeroed 2" high at 100 yards lasered at exactly 100 yards, explicitly stated, my group was centered 2" higher than my Point of Aim.
I then did the math and came up with that working out to a 205 yard zero

I input (Bullet details (BC etc.) are what vortex has programmed, I modified the velocity to my AV from above):
0.308 cal 147 grains bullet; 2725 ft/s; 205 yard zero
Ballistics Coefficient(BC) 0.398 BC Type G1
Caliber 0.308 Bullet Weight 147
Bullet Length 1 Muzzle Velocity 2725
Zero distance 205 Twist Direction right
Scope Height 1.75 Latitude 39.73209243604601
Longitude -91.06683254241943 Altitude 642
Barometric Pressure 30.09 Density Altitude(DA) 416
Absolute Pressure 29.4 Humidity 67
Temperature 54.3



I get:
(MOA/MOA scope with 1/8 MOA clicks)
Range___Drop__Drop_Drop_____Velocity___Time of Flight
Yards__MOA_Inches__1/8 MOA___Feet/Second___Seconds
100__1.86___1.95___14.87_______2502___0.115
200__0.12___0.25___0.95________2290___0.240
300__2.60___8.18___20.83_______2088___0.377
400__5.96___24.97___47.69______1897___0.528
500__9.95___52.09___79.59______1717___0.694
600__14.62__91.87___116.97_____1551___0.878


Then I shot a 200-300-600 across the course match.

I was dead on at 200y line, with the laser rangefinder saying it was actually 207 yards to my target.

At 300 with the laser rangefinder saying it was actually 301 yards to my target, my come up was SUPPOSED to be 2.60 MOA or 20.83 1/8 minute clicks - In reality I was right at 4.0 MOA up from my 200y zero. (I didn't right down the actual number of clicks)

At 600 with the laser rangefinder saying it was actually 609 yards to my target, my come up was SUPPOSED to be 14.62 MOA, or 116.97 1/8 minute clicks - In reality, (I think) I ended up 19.5 MOA up from my 200y zero (I left the turret dialed at 600, but have to go look at it, because I did not note the turret marking.  I will edit this post later with the actual turret marking and settings.  

All of this is with the same gun, that was zeroed and chronoed on the same day, The only deviation was the temp was 10 degrees warmer and the elevation was 100 feet higher.

I was going to compare Strelok, but I neglected to do so before, and had no signal at the range.

that is curious

because you're so far off at close range, it would take an extremely large deviation in BC to have that effect  (i.e. like a BC in the .2 range) and even then, it wouldn't match the 600 yard line experience

a velocity of 2350fps or so would actually match your results very closely.

so the first thing i'd do is start questioning the chronograph.   what type is it? how'd you set it up, etc

My numbers mirror your projected values.  On a calculator profile for my own .308 that I know is quite accurate.  I would begin by questioning your velocity numbers, or at least verifying them with another chronograph.  To be off 5 MOA from projected at 600 yards is extremely odd.

If I slow the MV down to 2500 and cut back the BC to .380 I almost duplicate your actual 300 and 600 values.  (Right on 300 but about 1 MOA off your 600 value)

My Chrono is a Chrony Beta, set up at the maximum distance that the cord allows (10 feet, I think?).  Those numbers were produced with a 22" DPMS AR10 and a 22" savage bolt gun.   They seemed in line with what I was expecting based on the published factory specs.  How do you test a chrono?

Anyone in Central IL with another chrono that we can set up to verify?

@barrysuperhawk

Chronograph Test

The above test makes me wonder if something screwy is going on with your velocity readings.

Someone in your HTF may be able to meet with you for a chrono test.

It really sounds like your scope is tracking wrong.  Using factory ammo that is being confirmed with a chrono, I can’t imagine why it would be almost 500 FPS lower as has been suggested.  The calculations your getting with your balisistics computer mirror my own calculations.

I don’t think your scope is moving as much as your telling it to.  Do a tracking test.

This is spot on for me most of the time if I get a good read of the wind.

For elevation it's money.

Attached File


ETA: outside of a match (which isn't a lot) I dial for dollars.