Un­der­stand­ing cold-bore zero

Make that first shot from your ri­fle count

Outdoor Life - - CONTENTS - by JOHN HAV­I­LAND


how ac­cu­rately their ri­fles fire 5-shot groups. How­ever, the true worth of a hunting ri­fle is how pre­cisely it places its first bul­let.

Sev­eral fac­tors can de­ter­mine if that ini­tial bul­let will fol­low your aim, but bore con­di­tion is per­haps most im­por­tant be­cause clean­ing sol­vent, oil, or foul­ing in a bore can act as a slight ob­struc­tion and cause a bul­let to fly some­where other than where it was aimed.

To test this as­ser­tion, I ran some of my ri­fles through a se­ries of 5-shot drills, each time mak­ing note of where the first shot landed in re­la­tion to the oth­ers. The first group was through a cleaned and oiled bar­rel. The next group was shot a cou­ple of hours later through the fouled bore after it had been al­lowed to cool. The third group was shot after al­low­ing the gun to sit for four days to give the foul­ing a chance to har­den and set. Fi­nally, I shot groups through a cold, clean bore that had the oil re­moved with de­greaser fol­lowed by some bare patches.

My CZ 527 Car­bine cham­bered in 7.62x39 is a handy deer-woods ri­fle. The ri­fle al­ways throws its first bul­let from a cold, clean, and oiled bore about 2.5 inches above where sub­se­quent bul­lets hit at 100 yards, and did so for this article. A cou­ple of hours later, the first and four fol­low­ing bul­lets formed a fairly tight group. Four days later, though, foul­ing in the bore had hard­ened, and once again the CZ shot its first bul­let 2.5 inches high. But the ri­fle fired its first bul­let only slightly high of four sub­se­quent bul­lets with its bore scrubbed clean, wiped with de­greaser on sev­eral patches to re­move sol­vent, and dried.

My CZ 527 Amer­i­can cham­bered in 6.5 Gren­del be­haved pretty much the same. Its cold, clean, and oiled bore flung the first bul­let about 2 inches above four fol­low­ing bul­lets. A cou­ple of hours later, the fouled bore placed the first bul­let only half an inch above the next four bul­lets. A clean and de­greased bore stacked five bul­lets on top of each other.

Bore con­di­tion does not seem to af­fect the ac­cu­racy of some ri­fles. A Sisk Ri­fles .22/250 of mine, based on a Stiller’s Pre­ci­sion Preda­tor ac­tion, groups Nosler 55-grain Var­maged­don bul­lets tight— from .5 to .76 inches—un­der any cir­cum­stances.

For the tight­est groups, how­ever, a clean bore with the oil and clean­ing sol­vent re­moved by de­greaser is the way to go. That will give you your best first shot.

A preda­tor hunter takes aim in West­ern Mon­tana.

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