If you are new to rifle shooting, one of the most challenging aspects about setting up a riflescope is getting it on ‘zero’ quickly. But what is ‘zero’? Simply explained, it is the range at which you can ideally shoot quarry using the centre of your crosshair, without any hold-over or hold-under (or windage allowance). All rifle projectiles have a ‘trajectory’. The path of travel from muzzle to target. It doesn’t matter whether air rifle, rimfire or centrefire. Put very basically, this is an arc dictated by the weight and speed of the projectile (let’s call it ‘ammo’). The heavier and slower the ammo, the greater the trajectory (arc). The faster and lighter the ammo, the flatter the trajectory. This whole concept can be difficult for newbies to visualise. Hawke Optics, understanding this, grabbed an already established shooting ‘app’ called Chairgun which air rifle shooters had been using for years … and have made it even better. Whether you own a Hawke Scope or not, this app can be downloaded free from the Hawke web site.
The app allows you to plug in various ‘scenarios’ and work out what is the best zero for your chosen ammo, but there are some basic things you may need to set up first, such as reticle type and projectile choice in the top menu.
Don’t worry if you’re not using a Hawke scope (though if you do, this app makes life really easy). If you use a standard mil-dot scope, you’ll find it’s equivalent within the app. Next, adjust the settings in the top section of the graph screen. 1. Ammo weight in grains. 2. Preferred zero range. 3. Your guns power output if you know it (in ft’ lbs). 4. Height from barrel centre to scope centre. 5. The magnification you normally set your scope at.
Once you’ve set these, the graph below the settings will adjust accordingly. The green arc shows the expected path of travel as seen through your scope. In this case a 16 grain pellet zeroed at 30 yards in an 11.8 ft/lb rifle. The arc shows that at 9 or 10 yards, you can use the centre crosshairs. At 20 yards, you will need to aim a bit low. At 30 yards, back to the crosshairs.
To exaggerate this, look at the graph for my .17HMR rimfire. The settings are clear above. A 17 grain bullet with a muzzle velocity of 2550 feet per second. A 105 yard primary zero. The scope set at 12x magnification. As you can see from this, I can shoot a one inch wide target from 25 to 120 yards.
But Chairgun has another clever tool too, one I use all the time when calculating adjustments and zero changes to rifles. This is the Intercept Applet. For me, the most important feature of this great app. set up the usual parameters as described above, select the Tools menu from the top toolbar. Then click ‘View Applets’. Another drop down menu appears. Click on ‘Intercept View’.
This will bring up a screen that shows the view through your chosen scope / reticle type. This example shows my Hawke SR6 scope set at 30 yards. As you can see, if I want to shoot a target at about 40 yards, I would need to use the aim point two marks down. For 50 yards, four marks down. Simple.
All of these pop-up reticle views can be printed via the right-click menu, though you need to set the print size. There is also a scope cap print option which prints a circular view that can be cut out and stuck inside a flip-up scope cover. Again, you need to play around with the print-size options .
Personally, I use the Intercept View, sized down to approximately credit-card size. I then keep it in a self-laminating ID card holder, kept in my pocket while shooting. An instant range reference when needed.
Copyright Ian Barnett, Wildscribbler, Dec 2018