The Crowning Act

Some years ago, the shop had completed a nice little Old Model Ruger revolver caliber conversion with dedicated .44 Russian chambers. If ever a gun should have shot well, this should have been it. Alas, on the first trip to the range, I would have been lucky to hit myself in the foot. There was no accounting for the awful accuracy. The rebore from Delta Gun Shop look great. It ranged perfectly. The forcing cone was in spec. Our reamer had a throat section of around .430″ which was spot on. Factory ammunition from Black Hills admitted no problems. I simply could not figure out why this gun shot so poorly. Giving it yet another hard look and thinking to myself the muzzle looked a bit odd, it finally dawned on me I had not yet crowned the barrel.

Ordinarily, most modern firearms feature precisely machined crowns that rarely ever give trouble, but the Ruger barrel had just been rebored and the bullets were now emerging from a flat crown that showed the usual ground/polished crown of the times. Without the usual 60-degree inner chamfer that trued up this surface, the remaining flat crown was hopelessly out of square and gave the predictably awful results.  The moral of the story is simple: When all else fails, check the crown.

A barrel’s crown is a small thing, but a poorly executed crown on any rifled barrel will have a devastating effect on accuracy. While I do not profess to have a thorough understanding of the dynamics of bullets exiting barrels, it requires little mental heavy lifting to recognize the problem. If the entire circumference of the heel of a bullet doesn’t exit the barrel at exactly the same time, subtle variations in gas pressure bearing on the bullet’s base and pressure from the barrel itself on the bearing area of the bullet can cause the bullet to tip slightly off its axis when it exists the barrel. Once tipped, the bullet will tend to wander off course more than usual. In short, the crown must be as square as possible with the bore axis.

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