Range Report Estimate new zero baed on know know velocity

[Deleted member 10043]

How can you determine a new zero if the muzzle velocity increases> Example 100 yard zero @2588 MV. If muzzle velocity increases to 2680 fps what would be the new estimated zero range? The only solution I can determine is based on bullet drop. Not to be confused with bullet path.

<span style="font-weight: bold">EDIT: JUST SCROLL DOWN TO LOWLIGHT'S POST AND BELOW TO GET TO THE CORRECT METHOD AND RESULTS.</span>

 

[Ledzep]

Re: Estimate new zero baed on know know velocity

Best I can come up with is find the difference at 100yd between their bullet drops, convert that to MOA/mil, then find a zero for the faster velocity round that is the same amount high at 100yd.

 

[Augustus]

Re: Estimate new zero baed on know know velocity

At 100 yds 92 fps difference in velocity will not produce a significant change in POI. There is no way to predict the effects of changes in barrel harmonics. The slower load may impact higher than the faster load.

If you establish a 100 yd zero for both loads their respective trajectories can be accurately predicted with ballistic programs. Go shoot, there is no substitute for range time.

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Augustus</div><div class="ubbcode-body">At 100 yds 92 fps difference in velocity will not produce a significant change in POI. There is no way to predict the effects of changes in barrel harmonics. The slower load may impact higher than the faster load.

If you establish a 100 yd zero for both loads their respective trajectories can be accurately predicted with ballistic programs. Go shoot, there is no substitute for range time. </div></div>

It does produce a material difference at long range if your zero is at 2588 fps and you switch ammo to 2680 fps. Example hand load 2588 fps with the same Sierra Matchking as the Federal Factory Match load. Harmonics are not part of the equation because we are estimating a new zero based on a calcuation(s). Also, the higher velocity doesn't even reach the lower lower known MV until passed 50 yards down range. In other words, the 2680 load doesn't slow down to 2588 until at about the 54 yard line.

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ledzep</div><div class="ubbcode-body">Best I can come up with is find the difference at 100yd between their bullet drops, convert that to MOA/mil, then find a zero for the faster velocity round that is the same amount high at 100yd. </div></div>

That is the best I can do as well. Looks like 107 yards for 2680 fps. That amounts to a 1 MOA difference @500 yards between the two velocities.

 

[Augustus]

Re: Estimate new zero baed on know know velocity

You can calculate all you want, you will not know where the two loads will actually strike in relation to each other at close range until you fire them. Harmonics have everything to do with it.

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity


You keep confusing close range for some reason with accuracy at long range. The original question is how to estimate the change in zero. Here would be a field exercise; I hand you a round and say the rifle is zeroed @100 yards for this round at 2588 fps. Fine. You hit your 5" target at five hundred yards with a simple reticle and iPod app. I hand you another round with the same type of bullet. I tell you this will fire at 2680 fps. What are you gong to do? You only get that shot. The OP or question is to emphasize <100 fps MV is material. How do you compensate? You don't have time like you suggest to set up two different zeroes. You pft calculating but ballistics is a science that is all about calculating. The OP wasn't aimed at Quincy Down Under. Though Quincy knew not to use ammo with velocities that varied. Still, the question persists.

 

[Augustus]

Re: Estimate new zero baed on know know velocity


Ok, in your example assuming both rds would hit within 1/2 min of each other at 100 yds, I would delete 2588, enter 2680, note the new solution, bam, splat.

The assumption I made about the two loads striking within 1/2 min. of each other at 100 yds is a very big leap of faith. It is not uncommon for different loads to deviate much more than that. Many times there will be a horizontal deviation added to the mix, therefore until both loads have a baseline zero established you are pissing in the wind attempting to predict trajectories at long range.

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity

They will hit much closer than 1 MOA at 100 yards. Anyway, you may still miss your 5" target target at 500 yards by 2.5". If you can't answer the original question I don't know why you are involved in this thread. You've stated your opinion. That's fine. I may still be incorrect but the question persists.

 

[Force_Multiplier]

Re: Estimate new zero baed on know know velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">
You keep confusing close range for some reason with accuracy at long range. The original question is how to estimate the change in zero. Here would be a field exercise; I hand you a round and say the rifle is zeroed @100 yards for this round at 2588 fps. Fine. You hit your 5" target at five hundred yards with a simple reticle and iPod app. I hand you another round with the same type of bullet. I tell you this will fire at 2680 fps. What are you gong to do? You only get that shot. The OP or question is to emphasize <100 fps MV is material. How do you compensate? You don't have time like you suggest to set up two different zeroes. You pft calculating but ballistics is a science that is all about calculating. The OP wasn't aimed at Quincy Down Under. Though Quincy knew not to use ammo with velocities that varied. Still, the question persists.</div></div>

I'm gonna miss... unless I'm lucky and the round impacts the same... because there is NO way I can predict what an unknown round will do

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity

But that is just it. It is not an unknown round. There is only one variable that is unknown. What to punch into your zero field on your app.

 

[Augustus]

Re: Estimate new zero baed on know know velocity

Culpepper, if you load two rds differently and one produces 100 fps more velocity than the other there is no way you can say with certainty that they will impact less than 1moa from each other at 100 yds.

The reason is that the bullets with different velocities may exit the muzzle at different points in the barrels cycle causing more dispersion than one would expect calculating the effects of gravity. As stated before some horizontal deviation may occur.

Anyway you just stated both rds strike within less than 1min from each other at 100 yds. That sir, is your zero that you will enter for both rds, the computer will give the solutions for extended ranges.

 

[Lowlight]

Re: Estimate new zero baed on know know velocity

Why is everyone always looking for a shortcut... the answer is you have to go out, shoot it ... the deviation is not exactly up and down in a specific direction.

you have to use the original zero, shoot it, then in the zero offset field you record the difference, along with the new MV.

It's like using a suppressor, and unfortunately not all software has the accounting for the zero offset.

 

[wnroscoe]

Re: Estimate new zero baed on know know velocity

One of the things I do is shoot in different temps at 100 yards through my chrono. I'm checking muzzle velocity and 100 yard zero at the same time. I use a Kestrel 4500NV during testing and record DA, Temp, Baro. Pressure and Alt.

So far, with a temp swing from 80 to 101 my zero has not changed and the velocity only increased a max of 20-30 fps. I've run the numbers and taken it to 1k each time. The down range dope changes slightly but, it's all realitive to a hard 100 yard zero, correct kestrel data input, good balistics calculator and range time to verify. When we move into winter and temps get to 30 degrees I'll have to increase my powder charge to get the same velocities but, again, range time, chrono and kestrel.

 

[Lowlight]

Re: Estimate new zero baed on know know velocity

With external forces, like Temperature change there is not really enough time to act on the bullet to move the impact.

Time of flight and distance is too short to move it and we have much better powders nowadays so they are not as temperature sensitive to give you huge changes.

 

[wnroscoe]

Re: Estimate new zero baed on know know velocity

Yea, 20 degrees isnt going to do much and at 100 yards and you better have a small pin point POA to detect any POI shift. I'm just checking to see where the temp change is to cause POI shift if any. In the past, for me, it's been around 60 degrees or more, summer to winter, and most of that was from a sharp velocity drop.

The only thing I use 100 yards for is chrono and 100 yard/knob zero, all other dope testing to confirm is at 600 yards +

There is no substitute for spent primers and range time.

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Augustus</div><div class="ubbcode-body">Culpepper, if you load two rds differently and one produces 100 fps more velocity than the other there is no way you can say with certainty that they will impact less than 1moa from each other at 100 yds.

The reason is that the bullets with different velocities may exit the muzzle at different points in the barrels cycle causing more dispersion than one would expect calculating the effects of gravity. As stated before some horizontal deviation may occur.

Anyway you just stated both rds strike within less than 1min from each other at 100 yds. That sir, is your zero that you will enter for both rds, the computer will give the solutions for extended ranges.

</div></div>

Okay, I'm stubborn but not that stubborn. I was approaching from the wrong perspective. Thanks. The zero field in the app doesn't change. Just change the speed. What the hell...

My signature fits me perfectly.

 

[MitchAlsup]

Re: Estimate new zero baed on know know velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Culpeper</div><div class="ubbcode-body">How can you determine a new zero if the muzzle velocity increases> Example 100 yard zero @2588 MV. If muzzle velocity increases to 2680 fps what would be the new estimated zero range? The only solution I can determine is based on bullet drop. Not to be confused with bullet path. </div></div>

Back to the original question at hand: Answer comes from Plaster "Ultimate Sniper"

You fire a number of rouonds at short range of loading 1 until the gun is properly zeroed. Ammo 1 is the std ammo (the go to load). Then you start shooting ammo 2 at the same range until you have a precise offset in both windage and elevation to re-zero the scope for ammo 2.

At this point you have the ability to re-zero the scope for either ammo 1 or ammo 2 and then each ammo has its own trajectory tables based on bullet BC, atmospheric parameters, angle, and range.

So, lets say the gun is currently zeroed for ammo 1 and you want to use ammo 2 for a long shot. Dial in the offset correctiion between ammo 1 and ammo 2, then dial in additionial adjustments for the range, angle, and wind conditions for ammo 2 from the ballistics chart/table/DOPE-book appropriate for ammo2.

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity

Thanks

 

[Deleted member 10043]

Re: Estimate new zero baed on know know velocity

Actual range trials. The zero at the higher velocity (2680) is 140 yards. So, when I use the usual factory ammo it is 140 yards and 100 yards with my lower velocity hand loads for my app. Since it is the same bullet I only need to change the zero data in the app for elevation adjustments. Works well out to 500 meters. That is as far as this particular range went out.

 

[Greg Langelius *]

Re: Estimate new zero baed on know know velocity

Frank is usually right, and this is no exception. You can't calculate your way to a hit, you have to put the system to work and find the real-time results.

There's more going on than just ballistics. Different velocities/barrel transit times will reflect different amounts of muzzle flip; i.e. the rifle points differently by the time the bullet emerges.

Keep in mind the difference between a 100yd zero and a 1000yd zero is about 1/2 of one degree; it doesn't take very much deviation at all to result in a completely different POI.

If you can calculate the effect of that, plus the ballistics, you're a better man than I am, Gunga Din...

Greg