Change in zero

[tspinaker]

This probably sounds like a stupid question, but lets say you zero your rifle and have all of the evironmental conditions recorded. Then the environmental conditions change, lets say the day of the match or whatever it may be. How do you account for those changes if you do not have the time or ability to rezero for the given conditions? Is this something ballistic software will account for?

 

[308pirate]

You don't re-zero a rifle because the weather changes. You have dope prepared ahead of time for various conditions or you use software.

You also don't need to account for minuscule changes in the weather, like a 50 ft change in elevation, 5F change in temperature, or .05 in Hg change in atmospheric pressure.

Running data on a solver for JBM where you can model the impact of atmospheric changes, plus (more importantly) keeping track of what you see downrange to build up experience will show you how big of an atmospheric change you need to worry about.

 

[SubOptimal]

As a counter question, how much dope have you obtained and how did you do it?
Zeroing you rifle is only the first step of many to develop valid data for the gun. That is data that will offer you a firing solution no matter the distance to the target or the environmental condition variables.
Start simple, pick a cartridge and a load, if you reload, so much the better but I really suggest starting with some form of factory match ammo to work with. That is my personal preference and others may disagree.
You would also need some form of ballistic calculator to aid you in estimating drops and wind holds. For simplicities sake, let's avoid wind holds for now unless you routinely shoot in very windy conditions. BTW, there is always wind but it complicates things and we are trying to build a basic data book.
More later, something just came up at the house.

 

[tspinaker]

I've gathered data for the load I'm currently using. I recently sold my .308 and picked up a 6.5 Creed, so I have a new rifle to gather data for. I've got my MV recorded and have been using the Hornady app for my comeups and wind for the local matches I shoot. I have been reading some about PRS and know that some guys travel all over the country for matches. So I was just wondering if the software takes the data for the conditions that you zero in and comes up with accurate datapoints for the changes in environment when the changes are more extreme. Or would you rezero in the new environment and put that data into a ballisics program. It would seem to me that there would be a shift in zero if you went from shooting in Montana to shooting in Texas, but I have not had that experience. I guess these would be two different talking points since the software will give a solution to the environment you're in. I'm just wondering the predictability of getting a first round hit when you change environments if you have not had a chance to reverify your zero in the new environment.

 

[joel65]

If you zero at 100 yds, then the environmentals have pretty much been removed from the equation. Doesn’t matter if you zero at 3700 feet and then take the same rifle to 600 feet.

 

[Deleted member 113831]

At 100 yards, temp and pressure won't make enough difference in your zero to matter. Light can..and will...mess you up though. Even at 100 yards, a different light comdition can mean a MOA or more change in zero.

 

[tspinaker]

Thanks, I appreciate all of the info.

 

[Deleted member 10043]

Some apps will account for zeroing weather and have an option for it. You can disable the function.

 

[seansmd]

I was wondering the same, if I zero for a particular load with a certain muzzle velocity and dial it in and set my zero stop. Then I change to a higher velocity round at he same distance I will not be able to lower my elevation. so do you re-zero for your new load @100 and set your zero stop?

 

[joel65]

I was wondering the same, if I zero for a particular load with a certain muzzle velocity and dial it in and set my zero stop. Then I change to a higher velocity round at he same distance I will not be able to lower my elevation. so do you re-zero for your new load @100 and set your zero stop?

... or change your stop so that it is not stop at zero . Your choice. Just need to make a decision for what works for you.

 

[Ledzep]

Check out the Hornady 4DOF app.

It uses a "zero angle" instead of a "zero distance". Your zero angle is the angle between your scope (set on "0") and the bullet as it exits the muzzle. Theoretically, that zero angle does not change, regardless of weather/conditions. Your POI at a "zero range" may change, however.

For example, say you shoot at 100yd, and your mean point of impact is .735" high. You go into the 4dof app, edit your profile for rifle info and use the "find zero angle" button. You input your parameters, then adjust the zero angle until it shows a .735" high impact. Save the profile, and from there on out, it tracks what to adjust your scope to for any conditions/range. You're scope set to "0" will likely always be a little high at 100yd in this example, but it doesn't really matter. If you were to plug in 100yd to the app with the same environmental conditions, it would tell you to dial down .2 mil to account for it.

Wind alone (aerodynamic jump) can cause several tenths of a mil in elevation change at the same baro/temp. Baro/temp changes can also change your impact point at the same range, even at 100yd.

1000 ways to skin the cat. I've had outstanding luck with the 4dof app, though. I set my zero angle at 1800ft, then shot a match at 5500-6000ft with no time to check anything, and had 1st round impacts all the way out to 1210yd. Likewise, when I moved back to SD @ 3000ft, I was within .2 mils at 1683yd (Far enough out with the creedmoor I was happy to be within a mil, honestly-- Trasol and Strelok were 1-2 mils off the mark on the same target), and hammering everything else I shot at that day (400, 600, 800).

The only downer is if they haven't shot your bullet with doppler yet.

 

[308pirate]

I was wondering the same, if I zero for a particular load with a certain muzzle velocity and dial it in and set my zero stop. Then I change to a higher velocity round at he same distance I will not be able to lower my elevation. so do you re-zero for your new load @100 and set your zero stop?

Set your zero stop so there is .5 mils / 1 MOA of downwards adjustment from zero. It will be obvious when you're not at your current zero, you won't be able to go 1 rev below zero and get lost (the real purpose of the zero stop), and you will have some wiggle room in case you have to re-zero for a minor change in ballistics.