September 23, 2010
By David Tubb
When it comes to setting zeros, you need a base from which to build.
By David Tubb
The sighting system on a high power competition rifle is crucial to attaining a shooter's best score, and it's the system I've most experimented with, modified and experimented with again. While my system has changed a good deal over the years, and I expect it will continue to change, the fundamentals of how to use it have not.
In high power, it's crucial to establish one zero to work from, and for the author it's his 300-yard rapid-fire setting. Each event has a unique sight setting, but they all start from this one.
Whether you're a service rifle or match rifle shooter, knowing your zeros is one fundamental that cannot be overlooked. The term "zero," as I'll use it here, means a sight setting that will--under excellent shooting conditions--result in a centered group on a target.
Since an across-the-course match includes four separate events, we may well have four separate sight settings. Few shooters will realize a centered shot group standing, for instance, using the setting they would have for the rapid-fire sitting event--even though both are fired at 200 yards on identical targets--because of how the rifle is held in each position.
Certainly, there will be different zeros at 300 yards and 600 yards due to bullet drop. Also, most shooters will be using different ammo for the different yard lines, and this in itself will influence impacts on the target.
I establish one zero to work from that I call my "no-wind zero." This is based on the 300-yard rapid-fire prone. In other words, when I dial my rear sight wind and elevation knobs to "0," I will have a centered group at 300 yards using my 300-yard ammo.
I use this as my baseline because it's fired prone at a short distance, and it's easy to keep up with. Zeros can also change due to barrel wear, and this 300-yard zero tactic clearly shows these changes.
Establishing my no-wind zero is a simple matter of shooting groups at 300 yards and adjusting wind and elevation until these groups are centered. Depending on the system you're using, this may have to all be done at the rear sight, or it may be possible to incorporate front sight adjustment to fine-tune the setting.
Ideally, "0" windage will be with the rear sight sitting in the center of its lateral adjustment range, which of course requires a front sight that can be moved left and right. The idea is to put the rear sight in the center of its range and then move the group's horizontal location to target center by shifting the front sight left or right.
Taking this a step farther, it's also ideal to have the rear sight elevation holding at a level that not only provides adequate elevation adjustment to go across the course but also that provides the shooter with the head position he desires. Accomplishing that goal requires the use of an elevation-adjustable front sight. When I have established my rear sight setting, I loosen the screws and position the rear sight knobs and scale plates to "0" to provide an easy index to my no-wind zero.
Over the past few seasons I have been using this type of front sight. Initially I was mostly interested in this design because it allowed me to have a higher rear sight mounting, but I now have come to rely on this feature not only to simplify my zero adjustments going from one yard line to the next but also to help maintain a more consistent head position. A well-designed, well-made elevation-adjustable front sight can be reliably adjusted to compensate for bullet drop, and this means the rear sight doesn't have to be moved nearly as much.
Since the elevation steps on the adjustable fronts I use are not as fine as the click-stops on my rear sight, there still may be a little change in elevation that must be dialed into the rear sight going from 300 to 600 yards, but it's a lot less than in years past. The steps on my front sight are each 0.050 inch, whereas a "quarter-minute" rear sight moves about 0.002 inch per click.
This front sight (shown with extra mounting base) allows the author to establish a rear sight height that gives him the head position he wants, without compromising on elevation adjustment for different yard lines.
The service rifle shooter, assuming he's using an AR-15, can't make such front sight elevation changes going from one yard line to the next, but he can use the front sight elevation adjustment to help establish his no-wind zero. Some service rifle modifications allow for wind adjustment in the front sight, but this is also only exploited during initial zeroing efforts. From that point, all elevation and wind adjustments must be done at the rear sight.
Of primary importance to the .223 Remington shooter is retaining as much upward elevation adjustment as possible, and this means that it's wise to establish an elevation zero for 300 yards that maintains a minimum but adequate amount of downward travel to get on target center for the 200-yard events.
The event zeros for standing and rapid-fire sitting are considerably different due to elements introduced by my shooting position preferences, but they are still recorded as changes from my 300-yard no-wind sight setting.
After establishing the no-wind zero (remember, it's for the 300-yard rapid-fire prone event), the other event zeros are likewise a matter of firing the event and settling on an index that produces a centered group in ideal shooting conditions. The zeros should then be recorded in your data book or, in my case, written on a strip of tape affixed to the rifle's stock tube.
To me, ideal or excellent conditions mean, primarily, the absence of wind. Good lighting conditions and moderate temperature are others. Essentially, no extremes. Trying to establish a zero on a day with even a light breeze is counterproductive. I'm usually working with my loads and have them going through a new barrel early in the spring, prior to the start of the shooting season. This is when I establish zero, and it's a matter of patience and timing to catch a day where I know zero will be accurate.
The wind will blow, the sun will glare, clouds and rain will come up, and it's going to get hotter and colder too. Along with these condition changes, the day's sight setting that will clean a target will also change. Having a place to start, though, is the only way to know which direction to head when faced with these changes. You will find also that having a
place to start is sometimes most important because it also gives you a place to return to.