This is an obvious exaggeration of reticle cant, but it quickly proves how difficult accurate shooting can be when the reticle is not perfectly perpendicular with the axis of the bore.

I was on the range when my cell phone started buzzing. It was Marc Bartoskewitz, a good friend and wildlife biologist from South Texas. He had been preparing for an upcoming caribou hunt--that meant a new rifle, new scope, and lots of long-range shooting practice--and I had been coaching from afar. Surmising the call might be important, I put down my rifle and picked up the phone.

"Man, I have a problem," Bartoskewitz said after exchanging pleasantries. "I just started shooting out past 300 and 400 yards, and my groups are way left, like 6 or 8 inches." He went on to explain that there was no wind, and the shots were from a bench. Bartoskewitz is pretty handy with a rifle, so I went through the checklist of possible problems.

"Who mounted the scope?" I asked from the top of the list.

He said he had installed the scope himself but without the aid of a leveling kit. We had the problem solved then and there. The riflescope's reticle was slightly canted--not perpendicular to the axis of the bore--and that was causing the strange windage shifts at longer ranges.

Most of us cant a rifle one way or the other when we shoot and usually introduce an error into the relationship between the scope's reticle and the axis of the bore trying to correct the problem. Since the rifle is tilted a few degrees left or right, most folks simply tilt the scope the other way so that it looks level when the rifle is shouldered. It takes someone who holds the rifle level or cants the opposite way to spot the problem.

A canted reticle or rifle is no big deal inside of 100 yards, but the longer the range, the bigger the problem. Unless it suffers from undue influences like wind or yaw, a bullet falls to the ground in a straight line. The vertical stadia of a ballistic compensating reticle or adjustments made via target turrets will not follow the same path as the falling bullet if the scope or rifle is canted. How bad can the problem get? With just 6 degrees of cant, a shooter induces over 36 inches of error at 1,000 yards. It is easy to see how Bartoskewitz was 6 to 8 inches off target, enough to miss a caribou at 300 to 400 yards.

To further illustrate the point, I loosened the rings on my Remington Model 700 Police and rolled the once perfectly perpendicular Leupold Mark 4 6.5-20X 50mm LR/T almost on its side, so the reticle was at a near 45-degree angle. I placed a target at 200 yards and shot the square, first making a 2-minute adjustment up, then 2 minutes right, 2 minutes down, and finally, 2 minutes left. As the photo of the square illustrates, a little cant goes a long way. Even sighting-in was a challenge, since corrections drifted along unusual paths all over the paper. Add conditions like wind or mirage to the equation and placing a bullet precisely becomes almost impossible.