Some scope manufacturers finally started to acknowledge the problem of the SFP reticle a few years ago. This took a while because manufacturers always try to make any new product appear as though it’s a simple solution to a complex problem: “Just put this dot on the target and pull the trigger!”
Zeiss was among the first optics companies to make the varying reticle size of second focal-plane reticles a virtue, by offering an on-line computer program to tell shooters the exact magnification where their Rapid-Z reticle would match the ballistics of their rifle.
Among the first companies coming to grips with the SFP reticle was Zeiss. They took the magnification-change “problem” and turned it into a virtue, devising a computer program that determined the precise magnification that your particular Zeiss scope should be set on to match the trajectory of your rifle’s load at 100, 200, 300, etc. yards. Then they put this program on their Web site, where anybody with Internet access can use it.
Soon other manufacturers did pretty much the same thing. These programs work well, but do have a couple of problems. First, the prescribed magnification may not be the one a shooter wants to use. It may be not enough for tiny ground squirrels, or it may be too much for today’s heat waves.
Also, unless adjusted for elevation, temperature, and barometric pressure, the program won’t be precisely accurate at the longer ranges where it’s really needed. The trajectory figures used to construct most ballistic predictions (whether an on-line computer program or the tables in reloading manuals) are calculated using a set of conditions called Range Standard: sea level, 59 degrees Fahrenheit, a barometer reading of 29.95 inches, and so on. (In fact, these are the standard conditions used in the trajectory tables in every reloading manual, the reason all the manuals are so agreeable.)
Swarovski offers a wide variety of reticles suitable for varmint hunting.
This means that unless we use scope rings to put the 6.5-20x on our prairie dog rifle precisely 1.5 inches above the bore (which may not be possible) and do all our prairie dog shooting on a California beach on 59-degree days (blatantly impossible), things aren’t going to work out all that precisely, especially beyond 300 yards. In reality the charts and tables provided by scope companies are entry-level suggestions, much like traffic laws in New York City.
One useful first step in using any ballistic reticle is to junk the notion that the dots or cross hairs will correspond precisely to where our bullet lands at 100, 200, 300, etc. yards. Instead we must go out and actually shoot our rifle to see where the bullets actually land. At 300 yards the second dot below the crosshairs (known to optimists as the 300-yard dot) may actually be two inches above where our bullets land.
This is not a disaster, or false advertising. Instead, it’s reality, and there are two ways to cope with it. One is to aim at the top of any prairie dog at 300 yards. Then, by shooting at other ranges we can figure out where the dots are actually sighted-in. They may be right on at 180, 270, and 360 yards, rather than 200, 300 and 400. So what? The readouts in our laser rangefinder aren’t limited to the nearest 100 yards.
Another solution is to adjust our scope three clicks down. With the standard ¼"-at-100-yards clicks, this amounts to 2.25" at 300 yards, close enough to actually sight-in the 300-yard dot at 300 yards. This obviously will change things at shorter ranges, but only 0.75" at 100 yards and 1.5" at 200. It also will probably put the longer-range dots closer to the “right” place.
The problem of the point of impact varying with every change in magnification is a little more complex. Aside from the obvious solution of leaving your scope on one power all the time, you can figure out how changing the magnification affects the reticle. If, for instance, you have a 6.5-20x scope on your rifle, cranking the magnification ring down to 10x will double the apparent distance between the aiming points. This means the “200-yard dot” is now valid for a longer distance.
In fact, long before the first ballistic reticles started appearing some friends and I used this principle when shooting ground squirrels at longer distance with 22 rimfires. All our scopes had simple plex-type reticles, and we discovered that the tip of the lower post could be a useful aiming point at longer ranges — often much longer than was then (or even now) considered practical for a 22 Long Rifle.
We also discovered that if we turned our scopes down from 9x to 6x, that the tip of the lower post became a precise aiming point at an even longer range. This was before laser rangefinders, but with practice (and there are lots of ground squirrels in certain parts of Montana) we became pretty adept at twisting the power rings on our scopes to shoot a distant gopher. However, a better solution for serious prairie dog shooting would be to create a ballistic chart for our scope at different magnifications.