IN SHOOTERS' parlance, most rifles go sour at some point in their working lives. That is, they suffer a loss of accuracy.
We looked at a few of the most likely causes in the last column (Dec. 23), so let's stay on that track.
There could be a bedding fault of some kind. "Bedding" refers to the places, areas and pressures of contact between the barrelled action and the stock.
Every barrel vibrates when a shot is fired, while the bullet is still in the bore. Good bedding achieves two things: it damps the barrel's vibrations when a shot is fired, and it helps the barrel to vibrate as uniformly as possible from shot to shot. Thus every bullet gets the best possible chance of leaving the muzzle on the same heading as its predecessors.
Poor bedding, however, does the opposite. It magnifies the vibrations and makes the vibration pattern erratic.
True, expert help may be needed, for the list of possible bedding faults is long. But a common flaw is that at least one of the bedding bolts (the bolts that hold the barrelled action in the stock) is either loose or incorrectly tensioned.
Some shooters call them stock screws, action screws or take-down screws. But they are bolts, not screws, and they are an integral part of every rifle's bedding system.
Ideally, we should tighten them with a small tension wrench, for the sake of precision and the ability to check or reproduce the bolt tensions whenever we want. No tension wrench? Then use these guidelines.
The front bolt should be firm but not wrenched into a death-like grip; go for "firm hand-tight", which usually serves well. The tension on the rear one should be slightly less, so begin with firm hand-tight and then back it off a fraction. If there is a middle bedding bolt, it should not be as tight as the other two.
Now for the secret: always tighten the rear or tang bolt last. If we ignore this rule, the close fit between the stock and the action's lower surfaces can be spoiled, and the bedding bolt problem will eventually recur.
The reasons, too long to spell out in detail here, derive from the fact that the barrel is both heavy and cantilevered.
In a small number of rifles, however, the front bedding bolt pulls down on the barrel instead of the action. Where this unusual layout exists, the rifle is often super-sensitive to the tension on the front bolt.
For example, loss of accuracy in the venerable Brno Model 2 rimfire and kindred rifles often stems from this sensitivity. A quarter-turn or less may fix it, but be sure to try both tightening and loosening. In such cases, one can adjust the front bolt without touching the remainder.
