How to keep rifles zeroed, assessing accuracy problems

Shooting Industry, Dec, 1989 by William Schumaker

How To Keep Rifles Zeroed, Assessing Accuracy Problems

One of the most aggravating facts of rifle shooting is when those tight groups you fired today, fail and scatter far and wide tomorrow or next week. Many inexperienced shooters panic and dump the rifle into some gunsmith's shop with multiple complaints and suggestions that the gunsmith who mounted the scope, barrelled the action, or made the stock, did a sloppy job!

Let's examine some of the causes of zero shifting. Improper sighting-in-originally is perhaps the major culprit. Example number 1: Shortly after WWII, during my learning gunsmithing days, a helper and I were building wildcat caliber .243 Rockchucker rifles on Mauser M-98 and 1903 Springfield actions. As no commercial 6mm's were available then, we used the .257 Roberts cartridge cases, sized the necks down to 6mm, and slightly onto the Roberts cartridge case shoulder to give a stiff fit for form firing into the improved, sharp-shouldered new design case.

These rifles were unusually accurate and potent deer-size game getters, as well as fantastic varminters at ranges well beyond 200 yards, where the .224 varminters and lighter bullets started to fall off to the wind and bullet drop. Tiring of building them for customers and firing only to sight in their scopes, we decided to build a pair for ourselves and partake of winter-time coyote hunting along the often winter-time frozen over Columbia river.

Our First Mistake

We zeroed in during the winter-time cold weather from a padded car-hood rest, as our outdoor benches were usually snow-covered and frozen. After a 3 1/2-mile drive to the range, the engine was always hot. Even with only six to 8-power scopes, mirage from the hot engine was visible. After a few rounds of firing the barrel, mirage (heat waves) from the barrel added to the engine heat magnifying the visible distortion!

As a small bore competitive target shooter, (mostly indoor competition), I failed to immediately place proper emphasis on this, although I'd also fired in many outdoor matches, even winning a few of them. But it was the wizards of the mirage and wind-breezes who reigned supreme on the competitive outdoor ranges.

My helper and I, pressed for time, eagerly awaited our chance for field testing these rifles on some of the deer-killing coyotes that frequent our area. We hurriedly sighted in over our car hoods' mirage, and hit the river breaks in the early mornings. At this point, we were too uninformed to understand the frequent, complete misses on standing shots, from medium to long range.

One evening Ollie stopped along a straight-to-the-mountain stretch of abandoned road and put up his portable target so we could verify our sighting-in. We were half-a-coyote off at a mere 150 yards. Then the bell rang to jog my memory into reality.

Later I shovelled the snow off and away from our range benches and puffed my way out to the 100-yard firing point. I slowly fired two shots. Both were off-center but near each other. I cleaned the barrel, allowed it to rest and cool for a few minutes, and then adjusted the scope. The next two shots were nearly center. I cleaned and cooled the barrel again. The third try placed the bullets almost center.

Now things were making sense. The next morning I again fired two shots, then made a slight adjustment. The third morning, a third 3-shot group pounded the bulls-eye. After this wake-up experience, we had much better luck on varmints. Then when we missed, we could usually determine why.

Hunters' Fast Sight-ins

Improper

In the hunting fields we seldom have opportunities for sustained on-going firing. Either the game has been spooked or hit and killed. Yet we found most hunters are so determined to get their guns sighted in accurately, that they shoot up several boxes of ammunition. These firing programs heat barrels, produce heat waves (mirage), poor accuracy and promote zeroing failure.

Mirage Moves Target Image

As the mirage tales of the deserts, mirage moves the image. In our case, it is the target image that is moved. A breeze or wind moves those heat waves faster and farther, and makes the result worse. You are aiming at an image that has been misplaced. Even with the world's most accurate rifles, mirage takes a formidable accuracy toll unless you are an experienced shooter who can read it and allow for it.

Unknowing gun owners get irked and snappy at times when we try to explain this. After all, they've hit lots of coyotes, rock chucks, deer, elk, etc., and resent being "told." Who the blazes are we to suggest their rifle might not be sighted in? However, these medium to large targets are no proof that their view of accuracy mechanics equals that of professionals. Some of these folks can learn much by listening a little. Furthermore they might even become addicted to the virtues of super-accurate target shootings, and "what leads to it."

Every contact of the action and barrel to the stock influences something! The new glass-type stocks are taking the accuracy-shooters by storm. This synthetic, non-shifting material, doesn't dry out, absorb moisture, redry, warp or constantly shift. A stable, large area bedding surface results between the barreled action and the stock. Some synthetic stocks even come in wood-grain finishes.