Shooting over distance requires you to adjust for bullet drop and windage. Calculating these corrections, or “dope,” ahead of time improves your chances for success.
My Opa learned over a lifetime of hunting to instinctively aim where he needed to cleanly hit his target. If he could see it, he could knock it down, quickly and humanely.
Unlike Opa I didn’t hunt to feed my family, so I lacked his motivation–and, sadly, his talent–to make every shot count by just looking.
As I mentioned in an earlier journal entry, I handload bullets to find the loads that work best in my guns.
That process involves testing each candidate for accuracy and precision at 100 yards. When I find a round that performs reasonably well, I zero the scope so it hits where I put the crosshairs at 100 yards.
To make a load useful in the real world, however, you’ll want to know what it’s going to do at ranges OTHER than exactly 100 yards.
I seem to recall from school that the longer a bullet is airborne, the further it drops due to gravity and the more time wind has to act on it. Time of flight to the target is determined by velocity; unfortunately, bullet velocity is not constant–the round slows from the time it leaves the barrel.
For those of us who lack the ability to solve calculus problems in our heads (or who don’t have access to computerized gunsights), it’s best to think about this stuff in advance.
One way to deal with all these variables is to choose a range over which the bullet’s trajectory remains within given bounds: that is, the bullet stays within an imaginary “pipe” of a given diameter.
This is the “Maximum Point Blank Range” approach, in which you decide how large your target is going to be and how far away it’s likely to be, then sight your rifle accordingly.
Knowing your bullet’s trajectory, you can calculate a range over which the round will stay in a “pipe” of given size. This is a good “set and forget” method that will allow you to hold dead on at all ranges up to about 300 yards (depending on your cartridge and the size of your target).
If you grew up hearing that you should zero your hunting rifles at 200 yards, then you’ll probably like the MPBR method.
Another method for shooting at further ranges is to simply adjust as you go, as if you were working with an artillery observer.
“Hmmmm, that was about three feet low,” says your trusty observer.
“Dern, I’ll raise the aimpoint three feet: let’s see, three feet is 36 inches, and at 600 yards 1 MOA is about 6 inches, so 36 inches is 6 MOA. Each click of the scope is 1/4 MOA, so that’s 24 clicks up…” say you.
And so on.
This method works well, assuming you have the time, patience, and rounds available to eventually hit your target (and assuming it’s still there when you’re finally zeroed in).
All of this is rendered somewhat moot by the existence of ballistic calculators that you can download onto your phone. Input your bullet’s weight, ballistic coefficient, muzzle velocity, etc.–remember, you collected all this information during your initial load development–and it will provide drop and windage corrections at whatever range you like.
However, I can imagine scenarios where my phone isn’t working or I just don’t have the time to refer to the app.
In such cases, it’s good to have “dope” calculated in advance. Furthermore, when possible, I like to test the calculator’s output against the actual performance of my load, in my rifle.
This is how I do it.
I’m a fan of Vortex Viper PST Gen II scopes, to the point where I now have them on almost all of my rifles. I also buy their “Defender” scope caps.
(note: these are Amazon affiliate links, which means that if you click the links and buy the associated products, Amazon pays me a fee–your cost is unaffected)
These scope caps ship with an insert on which you can jot down your pre-calculated dope. However, if you shoot more than one load through that rifle you’ll need an insert for each.
I took matters into my own hands and built my own scope “dope disks.” After running calculations for each of my loads across anticipated ranges, I recorded them on a spreadsheet.
Having determined that my scope caps would accept a 1.75″ insert, I adjusted the font and the size of each cell accordingly. I then covered the printed sheets with plastic laminate and put my secondary school art skills to use, tracing a (rough) 1.75″ circle around each entry and cutting it out.
The next step was to go to the range and validate my calculations. Our state-run range has a 500m steel target range, which enabled me to shoot and check the SBC app predictions against actual performance out to almost 600 yards.
I colored the distances I was able to verify in green, and plan to spend my range visits for the next few weeks happily plinking away, updating ballistics data for the rest of my loads. This facility also has a 1,000 yard range–run by a local club–that I hope will eventually help me extend my testing out past 500m.
In the meantime, I have verified dope for this load at distances up to half a kilometer, printed on the scope cap right in front of me. Now all I need to know is the target range–that’s what rangefinders are for–and some way to gauge the wind.
Hmmmm, maybe I should ask Santa for one of these…
