Some Members of Christchurch Gun Club will soon be taking up the challenge of shooting at 1200 Yards - We’ve been shooting 1000 Yards for a while and decided we wanted to make things even more challenging.
Many of us will be using .308 calibre rifles and so this distance will be truly pushing the limits (at this range our bullets will likely have dropped through the transonic and into subsonic speeds before hopefully hitting somewhere on the paper) and so we need to check whether we have the scope adjustment needed and have a rough idea of the windage and elevation settings we’ll need on the day.
To help our less nerdy members this post is going to be a guide to setting up a ballistic calculator, tweaking the settings so that the elevation readings match those of your scope, confirming you have the adjustment needed and then noting some useful information.
Ballistics involves a lot of variables (bullet weight, velocity, coefficient etc) fortunately most long-range shooters will know most of these, but there’s a good chance that you might not have measured your scope height (unless you’ve previously used a ballistic calculator) so go read my quick howto here:
You are also going to want to dig out any details you have on your velocity and scope settings at this point :-)
The ballistic calculator I’m going to use for this is JBM Ballistics (http://www.jbmballistics.com/cgi-bin/jbmtraj_drift-5.1.cgi)
So let’s dive right in and start inputting values
First off you need to select your bullet:
The library is pretty extensive - so you should just be able to select it in the dropdown and ignore all these other values (they’ll be ignored when you click calculate) - If there is a ‘Litz’ option for your bullet use it’ (If you are using a plastic tipped bullet and you want to be nosey about its stability factor you can add this here if you wish)
Next up we need to set our muzzle velocity… you do know it right? (if you don’t, take a best guess as we’ll be altering this anyway) Also set your sight height and barrel twist in this section
Kill the wind and target speed - you can play with these later
Set your Max range up to 1300 (I always prefer to see an extra row of data than I need), If you knopw your scopes true 0 range then set it here (otherwise we’ll be returning to this anyway)
Now for enviromentals we’re going to take a guess for the moment (as that’ll be good enough for now) but really these should be set to the values you’re shooting in - FYI the altitude for Bisley is about 200ft above sea-level
Now depending on what measurement your scope uses (MOA , Mil , cm/100m) you may need to change the column 2 units
Tick ‘mark sound barrier crossing’ - this is useful to see where you’re starting to run out of steam
Now hit calculate and you’ll get the ‘table of doom’
This data is useful… By looking at the 3rd column (drop) I can say that I’ll need an additional 13.2 MOA elevation on top of my 1000 yard scope setting.
My raw scope setting for the 1000 is 21.5 so with the the above I’d need to set the scope to 34.7 MOA… Now here’s an impotant note: My scope has an elevation range of 70 MOA (so 35 up and 35 down)… so you can see I am really pushing that limit…. But don’t panic Mr Mannering as the reticle has another 20 MOA of markings available for me to use.
This is something that’s important for you to check yourselves.
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