Range Report ballistic charts using one zero, multiple loads?

[lostinperiphery]

I'm wondering if is there a way, using a ballistic calculator(I have the iphone app "Ballistic"), to create a ballistic chart a load different from the one the rifle was zeroed with?

For example, my newest rifle is chambered in 300 AAC blackout. If I zero at 100yards with a 110grain bullet going 2400fps, but then wish to calculate point of impact for a 220grain bullet going 1015fps, is there a way to do this?

I hope that this question is not so basic as to make me seem idiotic, but please tell me if it is

I'm rather new to ballistic mathematics!

 

[CoryT]

Re: ballistic charts using one zero, multiple loads?

Determine the zero offset for the other rounf, for example .5 MOA high. Run the table and add or subtract the offset. JBM online has a zero offset box, Field Firing Solutions keeps multiple loads on file with their offsets and give you the correct turret setting on the fly.

 

[MitchAlsup]

Re: ballistic charts using one zero, multiple loads?

CoryT is correct: there is an offset to get from one zero to another, and then a drop/windage table for the different loading.

So, say gun is zeroed for load A, and you want to shoot load B. Take the offset of load B and dial that into the scope. Then take the drop/windage data for the chosen distance and dial that into the scope. The rifle is now shooting PoI = PoA at that distance.

 

[lostinperiphery]

Re: ballistic charts using one zero, multiple loads?

my ipod app "ballistic" has a field called "Y-intercept" (measured in inches) under sighting characteristics... is this likely the same as offset?

I'm not sure I understand how to determine offset itself, other than to simply put rounds on paper and measure. It seems to me that it should be fairly simple to calculate what that offset would be without ever firing a round, but the method eludes me...

 

[lostinperiphery]

Re: ballistic charts using one zero, multiple loads?

perhaps I figured it out using JBM' online calculator. It has a few features that my ipod app did not... let me know if this makes sense, or if there is a simpler way that my app might be able to handle

FOR EXAMPLE: my 300blk to compare supersonic 110grain, vs subsonic 220grain, if the rifle is zeroed with the 110grain...

--Run a typical ballistic chart for 110grain .308 @ 2400fps
zero range: 100yards
check box for "elevation correction at zero range"

--in the output for the above load, find under output data "Elevation"... This is what the software calculated to be the angle of the barrel relative to the optic, based on our zero range. We will be able to use this data in the next step to 'lock' this zero setting... (in this case it's 4.639 MOA)

--Run a modified ballistic chart for 220grain .308 @ 1015fps
-zero range: irrelevant
-under "Elevation" input what you just found... (again, 4.639MOA in this case)
-DESELECT "elevation correction at zero range". Software will ignore zero range, and instead calculate based on that elevation angle between the optic and barrel


In this case, the 220 grain @ 1015fps showed to be 14.3" low, and the slow moving bullet never even crosses the line of site.

 

[gstaylorg]

Re: ballistic charts using one zero, multiple loads?

You probably want to use the same 100 yd zero setting for both; it will make it easier. All you need to do is know the MVs for both rounds AND the relative POIs for the other rounds when zeroed at 100 yd using round #1. For example, round #2 is 0.3 MOA low and 0.2 MOA left at 100 yd when fired using the scope settings for the 100 yd zero of round #1. In this scenario, whatever your ballistic calculator tells you your drop should be for round #2 at some specified distance, you correct it for the difference in the 100 yd zero from round #1. In the example above, if the calculator tells you to use 10.0 MOA for round #2 at 500 yd, you would actually use 10.3 MOA because the round #2 was already 0.3 MOA low when the rifle was zeroed with round #1.

Bottom line is that you need to know the MVs for each round and how the relative zeroes compare for each round at some specified distance. Then you can correct for the difference in the POI for a specific round when the rifle has been zeroed using a different round. It's just a way to correct to get the same approximate "starting point", then you use the ballistic data from the calculator. Just be aware that zeroes can change depending on conditions and that ballistic calculator windage and drop charts may not always be dead on, depending on how good your input data were. However, this approach should usually get you close, or at the very least be a good starting point.

 

[lostinperiphery]

Re: ballistic charts using one zero, multiple loads?

Thanks gstaylorg, that makes alot of sense... I probably should've prefaced with the reason I began wondering about the topic. I was trying to determine what would be the most appropriate range to zero my eotech. Or rather, if I did zero at 100y, or 50y or 30y, with supersonic, how differently would that affect my POA inside of 200 yards or so for subsonic. Thus, I was trying to figure out a way to compare trajectories before I even got to the range, haha.

Your method makes alot of sense, in that your running calculations based of your actual results. I guess I was just trying to save ammo by doing it all 'theoretically' ahead of time

...

 

[Greg Langelius *]

Re: ballistic charts using one zero, multiple loads?

CoryT and I use the same method. My implement is the Pejsa Spreadsheet Stock Table.

 

[gstaylorg]

Re: ballistic charts using one zero, multiple loads?

Establishing good MV data and zeros at a specific range are where you want to start. This will give you an internal reference or "starting point" between your different loads. But I'll emphasize again that the ballistic calculators will only give info that is as good as the data you input. Typically, the more you shoot with different loads, the better your input data will be, and the better the calculated output will be, or maybe I should say the closer it will be to what you actually determine when shooting at various distances. There are many of members here that are far more expert than I on the use of ballistic calculation engines, several have actually written the software. I have had pretty good results using JBM, I think in part because I am very meticulous about recording shooting data so that my input data is solid. For example, I shot for the first time in a competition at 1000 yd last weekend. Prior to that, I only had drop data out to ~890 yd. Even so, the drop predicted by JBM for that rifle/load was within one "click" (0.125 MOA) of the elevation it actually took to get in the X-ring. Anyhow, good luck with with your shooting.