Reach new heights! Achieving a more consistent aim might just be a case of adjusting the height of your scope, says Andy McLachlan
The relationship between the centreline of your scope and barrel is a crucial dimension for shooters wishing to see their aiming points fall into line with the appropriate aiming marks within the scope’s reticle. This is an important issue that can often be overlooked by shooters.
Without going into too much detail, if your scope is mounted low in relation to the barrel’s centreline, the scope’s aiming points will then allow you to plot a relatively flat trajectory up to about 30 yards, which is fine if that or something close to it is likely to be your average shooting range.
For decades, I mounted my scopes so that they tended to be 1.6 inches or 41mm above the barrel centre line (BCL). If, like me, you prefer an uncluttered reticle for hunting, such as the classic 30/30 we all knew and loved for decades, this is not such a problem.
Rather than using particular aiming marks within your scope, you will have to rely upon good old holdover and under as the pellet flies towards the designated zero range – and, of course, for when the pellet starts to drop due to the effect of gravity.
However, if you want to use a more target-orientated scope that contains some useful additional aim points, such as the many milliradian and minute of angle reticles, you will need to ensure that the scope is mounted at the correct height, allowing your additional aiming points to coincide with your chosen zero range.
For example, many of my shooting friends who are involved in shooting HFT to the highest standard keep to a trusted format regarding scope and mount choice. All use scopes with 30mm body tubes as, with the odd exception, most high-quality scopes are designed with this diameter rather than the smaller, more traditional 25mm (1 inch) tube size.
For the scope reference points to correspond with the trajectory of an 8.4 grain .177 pellet flying at 785 feet per second (fps), it is necessary to mount the scope 2.2 inches (57mm) above the BCL to maximise pellet trajectory, with set aiming points visible in the reticle.
If your gun is set at this velocity, and zeroed at 40 yards using something like the ubiquitous JSB Exact, you will find that you have some useful scope reference markers for most of the targets between eight and 45 yards that will be encountered on an HFT course.
If you zero your combination at 40 yards, the first half-mil marker above the crosshair on a milliradian scope will correspond to ranges between just over 20 and 30 yards. At this point, it will normally be travelling at about a pellet’s width above the first half-mil marker prior to its descent to the zero 40-yard crosshair aiming point.
However, if you try to compromise by fitting as many aiming points surrounding your estimated range as possible into the kill zone, you will more than likely knock the target over, presuming that you have considered any effects the breeze may have upon your shot placement.
The first half-mil marker below the crosshair, with all the variables set as above, will then correspond to your maximum range of 45 yards. The 35-yard mark will be above the crosshair in between the first half-mil mark and the crosshairs. Close-range targets of eight yards will be in the region of 2.5 mils, with 10 yards about 1.5 (both below the crosshair).
The information I have provided above corresponds to milliradian scope reticles. Minute-of-angle reticles have larger spacings between each mark, and will not work in the same way.
The excellent Hawke ChairGun ballistics software (www.hawkeoptics.com/chairgun.html) allows you to experiment with scope height: it only includes Hawke scope reticles, although you may find one that is very close to your own! It is one thing for me to write about this and state 100% that your own aim points will correspond perfectly if you decide to use my suggested settings.
That can only be confirmed by shooting, preferably at an indoor range at least 45 yards long, and with the ability to move targets around to your preferred aiming point distances and plotting your own pellet trajectory chart. I do feel confident, however, that should you decide to try this arrangement, you won’t be too far off, if at all.
There are two scope mounts that are suitable for this system. The first one, and the preferred choice of my son James, is the Sportsmatch ATP 66 (£68). The 66 also has the advantage of allowing you to actually adjust the mounts laterally yourself for zeroing purposes and, minimally, for height. I and a few others use the BKL-301 (£55). The BKL is 1mm less in height, but that has only very minimal effect, if any, on settings.
So, there you have it. I can confirm that this setup will allow you to maximise the usefulness of your milliradian scope’s aiming marks. All any of us need to do now is make sure we practise frequently and learn those aiming points off by heart.
If you struggle to remember the settings, just write all the reference points on a piece of card and take it with you to the shoot.
More on airgun aiming
- Zeroing a scope: The ultimate how-to
- How to improve your airgun’s accuracy
- Re-zeroing a rifle: Ask the experts
- Tips on garden plinking with Mike Morton
- Plinking: Best options for garden range