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Discussion Starter #1
We are shooting a .300 RUM
Zero at 200 yards.
According to various ballistic calculators.
At 500 yards it calculates a bullet drop of 32.4 inches.
A custom elevation turret was ordered to all the correct specifications to a very reputable company.
Gave ALL applicable data, velocity, bullet weight, BC, etc.
Set 2 targets at 200 yards. The top one was exactly 32.4 inches above it.
Turned the turret to 500 yards, fired at the bottom target.
I was assuming the bullet would hit the top target, right on.
Not on the paper and no idea where it's hitting.
Am I making the wrong assumption, or is there a problem with the turret, or even the ballistic calculator data?
Any and all responses would be appreciated.
Thank you!
 

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To start,

Did you verify your calculations by testing actual drops on target (at 500m) before you did this?

Did you do a box test on the scope so that you know how much 40 clicks (for example) actually moves POI?
 

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The fact that the bullet drops 32 inches at 500 yards does NOT mean its 32 inches above the line of sight at 200. Ask your calculator for the 'mid-range' when zeroed at 500, then calculate back from there to set your upper target.
Most do it backwards and zero at 500 and then shoot at closer range to get the 'actual' measurements instead of calculations.

I would instinctively say, look for the bullet hole about about 8 inches high at 200 yards.
 

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Simple fact: your bullet drops way more the 2nd 250 yards, than it did the first 250.

Your idea makes sense as a mathmatical equation, but we're talking ballistics and trajectories, not mathmatical equations. Simply put, that bullet drops way more during the 2nd 250, than during the initial/closer 250yards.
 

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Simple fact: your bullet drops way more the 2nd 250 yards, than it did the first 250.

Your idea makes sense as a mathmatical equation, but we're talking ballistics and trajectories, not mathmatical equations. Simply put, that bullet drops way more during the 2nd 250, than during the initial/closer 250yards.
Really? Hmmm. You're right about the rate that the bullet drops at but your statement about mathematical equations is way off in the ozone. Anybody that has used a bullet drop calculator knows that the mathematics works pretty well...if you use them correctly.
 

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I disagree. If you use a ballistic calculator, it works. But not for normal basic mathmatical equations.
 

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To continue on with where I think MZ5 was going...
There is a difference between actual, and company marketing. Similarly there is a difference in BC if using the wrong system for a given bullet.

For an example: 190gr SMK
Say you gave the turret folks the top G1 BC, but the powder you are using can't get you there. When zeroed at 100, here's your difference.

99790


99791
 
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Jack is correct, it's approximately 8 - 9 minutes of elevation for a modern centerfire magnum when zeroed at 200yds. The reason I know this is in hp silhouette the chickens are 219yds, pigs 330yds, turkeys 421yds and rams 547yds. The 6.5's, 7mm's and 30's have similar trajectory's with the 6.5's being the best and the 30's having the most drop and wind drift. A 308win has about 8-9 minutes of elevation at the turkey target but it's approximately 500fps slower than a full power 300 load, using the generic math of 12yds per 100fps that would bring it right up around 2950fps for a 170-180 bullet.
Fyi a 260 has about 3 minutes less drop at 547yds than a 308 or about 16".
 

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Discussion Starter #11
To continue on with where I think MZ5 was going...
There is a difference between actual, and company marketing. Similarly there is a difference in BC if using the wrong system for a given bullet.

For an example: 190gr SMK
Say you gave the turret folks the top G1 BC, but the powder you are using can't get you there. When zeroed at 100, here's your difference.

View attachment 99790

View attachment 99791
Very useful information.
Thank you for going through the trouble of the example.
I appreciate it.
 

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For simplicity I used 32” drop.
Assuming the turret is correct and zeroed on the 200yd mark then Assuming in/100yd, the elevation is 32/5=6.4. At 200yd 6.4*2=12.8”. In MOA, 32/5/1.047=6.1 MOA, at 200yds 6.1*2*1.047=12.8”

You should be able to duplicate this in you Ballistic Calc by setting the zero at 500yds and looking at 200yd rise.

Drops are relative to line of sight, so you raise the line of sight 32” at 500 yds, At 200yds its less.
 

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At 500 yards, it calculates a bullet drop of 32.4 inches…
…Set 2 targets at 200 yards. The top one was exactly 32.4 inches above it.
That's your math error. You are thinking that if the bullet drops 32.4 inches at 500 yards, it will be 32.4 inches high at 200 yards. It won't. Doom has it right. Trajectories diverge as a matter of their angles, and not by fixed widths, with the origin (vertex) of the angles being the scope image at the firing point. That is, 32.4 inches at 500 yards is the distance between the sides of an angle from the scope image of 6.188 minutes. At 200 yards, the sides of that 6.188-minute angle will be just 12.96 inches apart, not 32.4 inches apart as they are at 500 yards. So your bullet will impact 12.96 inches high at 200 yards, where it is probably going through an old hole in the target backer between your two targets.

The reason this happens is that your scope is dumb and doesn't know what range your brain is concerning itself with. Its adjustments just move the point of impact (POI) a certain distance across the image in the scope. Well, the image of a 32.4 inch span is smaller from 500 yards than it is from 200 yards, where it is the same size as a 12.96 inch span, so that is how much the same 6.188 minutes adjustment will move the POI at those two ranges, respectively.

To solve the problem without invoking angles directly, just use the ratio of the ranges:

32.4 inches × 200 yards / 500 yards = 12.96 inches (the yards cancel out)

You can confirm your custom turret calibration by dividing 6.188 moa by the number of moa in each click of your sight changes the point of aim and checking that they match.

Example: suppose you have the most common 1/4 moa clicks:

6.188 moa / 0.25 moa/click = 24.75 clicks (the moa cancel out)

That rounds to 25 clicks, so you then expect your 500-yard setting to be 25 clicks above your 200-yard setting if it is correctly scaled for your bullet and muzzle velocity. With half moa clicks, it will round to 12 clicks. With 1/8 moa clicks, it will round to 50 clicks. With 1/10 moa clicks, it will round to 62 clicks.

If you need to solve this for other ranges, the exact moa are:

Inches of Span / (π × Range in Yards / 300) = moa
 

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OUCH ! ! I'm getting a headache... the elliptical shape of the trajectory you are discussing has it's own formula, which is easily googled.
 

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There is some terminology that is being abused here.
If you extend a straight line from the center of the bore that is where "bullet drop" is measured from.
If you extend a line through the center of the scope or sights that is "line of sight" where the bullet path is measured from.
Bullet drop is always below the bore center because gravity starts working on it as it leaves the barrel.
Bullet path will start below the line of sight rise up to some point above the line of sight and then drop down below the line of sight.
I think that this discussion might be using bullet drop in reference to the line of sight which wont work.
 

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prostreet, unclenick's math is always fascinating and always correct but it went over my head like Maverick and Goose doing a flyby at Miramar.

I on the other hand am very poor at math and do things the hard way, by shooting.

If I understand what I read correctly, there was no mention of bullet wieght?

For my example I will use a 180 grain Accubond fired at 3274 fps from my Sendero SFII 300RUM with a 6.5-20X50 SFP Simmons Whitetail Classic sighted in 3" high at 100 yards (scope center is 1 7/8" above barrel center) it's " dead on" at 300 and 19 - 20" low at 500 on the particular day of testing in a 10-15 mph crosswind. Hornady's ballistic calculator said it would be 18" inches low. I should add that the tests were not done on the same day.

I prefer not to "twiddle" with scope adjustments and instead rely on "hold over" at known ranges but that's just me.



The wee hole to the right of the group is from my . 243 during a sudden lull in the wind while aiming at a target to the immediate right.

RJ
 
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There wasn't any need to consider the bullet or the trajectory because he already had established it would impact 32.4 inches low if you aimed at the 500-yard target using a 200-yard zero. So all that has to be figured is how things will look through the sights. 32.4 inches at 500 yards will cover the same portion of the field of view that 12.96 inches cover at 200 yards at the same magnification. Thus, correction for 32.4 inches at 500 will correct for 12.96 inches at 200, and the OP's bullet will be impacting that much higher at 200 if his custom elevation knob is correctly calibrated for 500.
 
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There is some terminology that is being abused here.
If you extend a straight line from the center of the bore that is where "bullet drop" is measured from.
If you extend a line through the center of the scope or sights that is "line of sight" where the bullet path is measured from.
Bullet drop is always below the bore center because gravity starts working on it as it leaves the barrel.
Bullet path will start below the line of sight rise up to some point above the line of sight and then drop down below the line of sight.
I think that this discussion might be using bullet drop in reference to the line of sight which wont work.
To clarify Unclenick and I both assumed the drop was relative to line of sight and the math works, on the assumption that the 32.4” drop is relative to line of sight.
 

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Right. Just to check, I ran a 175-grain SMK at a little over 3200 fps (a reasonable number for the RUM) in a ballistics program with the zero at 200, and that did impact in the range of -32" at 500, so that confirmed this is what the OP was talking about.

Incidentally, since most ballistics software shows how far above and below zero the bullet is at different ranges, the non-mathematical solution is simply to change the zero to 500 yards and see how high the bullet is at 200. Spoiler alert: It's the same 13" the calculations show.
 
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