What specification should you go for when choosing your new telescopic sight? Possibly price is the major factor. Do you need maximum light-gathering capability? How large a magnification do you go for? And then, for those longer-range shots, should you be looking at a graduated reticle or an adjustable elevation turret?
In this brief article we will concentrate on the reticle/turret choice. Why should you go for one option over the other?
For our ‘scope, we will choose Swarovski’s popular Z6 2.5-15×56, which is available with or without a Ballistic Turret (BT). Without the BT, your choice of reticles includes graduated versions: giving you positive ‘aim off’ points for long range shooting. We will be mounting the ‘scope on a .308 rifle, shooting Norma 150g Ballistic Tip ammunition.
The concept of the BT is easy to understand, and relatively simple to set up (read more…). Essentially: you zero the ‘scope at, say, 100m. You also want longer-range zeros at, say, 200m, 250m & 300m. Having got your base, 100m, zero, you then re-zero at 200m and drop the ‘green dot’ ring onto the turret; then do the same at 250m with the ‘yellow dot’, and 300m with the ‘red dot’. If you don’t have range facilities that allow you enough distance for the longer range zeros, Swarovski’s website offers a Ballistic Program that will work it all out for you.
So, out in the field, you’ve ranged your target at 250m, you just turn the BT until the yellow dot is in line with your zero marker, place the cross hairs on your desired point of impact, and squeeze the trigger.
The reticle is set in the second image plane. This means that, whatever the magnification, the reticle remains the same size. So, any zero points – altered by turning the BT – will remain constant, whatever the magnification.
Please note my repeated use of the phrase ‘whatever the magnification’!
Now let’s concentrate on the graduated BRX reticle. Again, the concept is simple to understand. Go to the range, & obtain your base zero – let’s go for 100m again. You can then either shoot at various long ranges and discover what distances the graduations relate to, or you can go to the Swarovski website and get the Ballistic Program to work it all out for you.
So, setting up the BRX reticle was simple, wasn’t it? Well, yes, but…..
Because the reticle is in that second image plane, the reticle remains a constant size whatever the magnification. Like the BT your 100m base zero will always be dead centre on the reticle cross hairs. However, as you vary the ‘scopes magnification, although the BRX reticle remains constant, your view through the ‘scope of the target and its surroundings will expand or contract accordingly. This will directly affect the calibration of those graduations.
The following graphics illustrate this point. In the first, our ‘scope is set at 15x magnification. In the second, we’ve reduced magnification to 10x. In each case base zero is 100m, but look at the remarkable difference in those down-range readings.
I’m not saying that there is anything ‘wrong’ with a graduated reticle in the second image plane. It’s just that you must be well aware of the consequences that varying the ‘scopes magnification can have on long range shot placement.
In all likelihood, if you are taking a long range shot, magnification is going to be wound right up. But that’s not always the case. If you are likely to make use of a variety of magnifications, ensure you are prepared for the consequences with notes on all possible ballistics permutations. Swarovski does include a sheet of appropriately marked stickers with BT and graduated reticle ‘scopes, and these can be quickly referred to whenever necessary.
So why am I telling you this cautionary tale?
Well, to cut a long story short, I had stalked into a good whitetail buck that was less than 50m away in some scrub. I had reduced the magnification so that I could easily spot him and the three or four does that he was courting. He started turning to present a perfect shooting opportunity, and I eased off the safety catch. As I took initial pressure on the trigger, and with a beautifully wide field of view at the low magnification, I saw a monster whitetail come over the ridge in the background, some considerable distance away. I was straight on to him, but he was straight into the undergrowth. All I could see were the tips of his antlers, and the occasional flash of some part of his body. Not all was lost: there ahead of him was a small clearing. If he came into that space…. and there he was! As I whistled to stop him, the sights were already on the edge of his shoulder. I squeezed the trigger – and shot straight over the top of his back. Needless to say, he didn’t give me a second chance.
Feeling rather deflated, I tried to analyse what had gone wrong. I had been in a rock-solid shooting position. Despite the size of the buck, my breathing had been steady, and my heart hadn’t been racing. Then it slowly dawned on me. I leant forward and took a look at the zoom ring on my Z6. My ballistic calculations were all set for 15x, and I had used the second graduation down (the first dot) as my aim point. With my home-loaded .260 ammunition, this equates to just over 260m. However, with my ‘scope set at nearly 6x magnification, that second graduation represents a point of impact at more like 430m.
I learned a lesson the hard way. Hopefully this advice will save you the same heartache!