This article was edited from software documentation to encourage a discussion about sight cant. If you are an experienced long range shooter, some of the article's contents may not be new. FIRST, SOME BACKGROUND In the 1800's a quality rifle was often equipped with a front sight level. Old timers understood the high trajectories of the day made it necessary to hold the bore and sights perfectly vertical. Smokeless powder and modern boat tail bullets introduced at the turn of the century shot much flatter. Since a typical shot rarely exceeded 250 or 300 yards, well within acceptable point blank ranges for most hunting rifles; sight levels disappeared as common long range shooting equipment and most shooters forgot what the old timers had learned. For much of this century the gurus of accuracy have been the bench rest crowd. Benchresters pound their wide flat forearm rifles into sand bags and shoot at fixed ranges. Since they are trying to place shots in one hole and shot-to-shot sight cant does not change; cant wasn't an issue. Modern varmint and long range shooters are hitting targets at ranges beyond 1000 yards. At these ranges all load have high trajectories and serious so shooters have rediscovered the importance of sight cant. New variations of the old timer's sight levels have been adapted for use with scopes and some new scope designs have internal levels. BULLET IMPACT WITH CANT Canting a firearm only a few degrees from true vertical can significantly change the bullet's point of impact. Canting to the right moves the point of impact to the right and to the left moves the point of impact left. If a firearm is held in the same canted position with every shot, but zeroed at a specific range, tight groups can be maintained at the zeroed range but the arm will shoot right or left of the LOS at other ranges. If you have never thought about cant before, then consider this. At 300 yards, the affect of cant is enough to give small critters a new lease on life. At long ranges, canting only 12 degrees (equal to 2 minutes on a clock) may open a group horizontally as much as a 10% powder charge variation does vertically! WHO SHOULD CARE? Even if you shoot to distances less than 300 yards there are aspects of cant that may be important to you. If you shoot quarter size groups at 100 yards and never bang away at distant targets, 12 degrees of cant can still add 50% to your horizontal group dimension (or shrink the group size by 50% if you are canting). When I first bought an anti-cant bubble I discovered the answer to a puzzle that had been making me nuts for years. I had several hunting rifles that would zero nicely, but when fired at longer ranges the groups always moved horizontally. It was suggested that this was caused by poor quality bullets, a cheap production barrel and my shooting. When I installed the cant bubble the reason was obvious. I tip all guns with monte carlo stocks to the right! To make matters worse, like many people, I had twisted the scopes so that the crosshairs were vertical. I had effectively screwed up the scope mounting so the bore was no longer directly under the line-of-sight! Whenever I zeroed to a set range everything was fine, but when shooting well beyond the zero range, the built-in cant would move groups horizontally. Dumb I know, but since discussing this with others I have found I am not the only one to do this. Once I starting watching the affects of cant I began to understand it is one of the most important accuracy issues that a varminter can control. Here's an interesting test suggested by Dave Beisner (designer of the first anti-cant bubble device). Shoot your best group at a standard target, then shoot at a round target staked to the ground to eliminate any vertical or horizontal edges. Most people discover their groups open up when fired at a target that has no horizontal or vertical reference. This is because everyone subconsciously lines up the crosshairs to the edges of the paper or target frame; effectively eliminating shot to shot cant variation. Most shooters will cant slightly left or right with each shot (except those with flat bottom rifles pounded into bags) resulting in groups with more horizontal spread than if cant is eliminated. The affect of cant is much more pronounced at longer ranges when velocities fall off and the trajectory steepens. A 30-06 hunting load zeroed to 100 yards may shoot 2 feet to the right at 600 yards if canted only12 degrees; and 9 feet at 1000 yards! The cumulative cant and normal free-hand shooter errors can easily put a shot outside the vital zone. WHICH BUBBLE? I have tried a couple different cant bubbles and stayed with the original developed by Dave Beisner called the ACD or Anti-Cant Device. The determination of which level works best for you may depend on how you shoot. The ACD is a simple scope ring modified to accept a bubble from a common carpenters level. When mounted on top of the scope just behind the elevation turret I can see the bubble with my left eye while looking thru the scope with my right. It is simple and tough enough to hold up in the field, and even works when the scope is fitted with Butler Creek flip-up caps. A "must have" item is a little gadget from Straight Shot, LLC (http://www.straightshotllc.com) called the Reticle Leveler. It will ensure your scopes are mounted so the reticle is perfectly vertical & horizontal with the bore. The Reticle Leveler is available from Brownell's, Midway, etc. or you can order one direct from their web site. Jim Ristow, Recreational Software, Inc. info@shootingsoftware.com http://www.shootingsoftware.com