Recently someone asked me: “How many rounds does it take for a rifle to break in and really start shooting?”
From my observations over the past 10 years or so, it takes maybe 20 shots at the very most, and usually none at all. Back in the good old days, before the advent of rigid receivers and bolts, pillar bedding, synthetic stocks, epoxy, bedding girders, and chassis stocks, the average hunting rifle was stocked in wood, often of a dubious quality, and poorly bedded. When it was shot, it did a lot of twisting, squirming, writhing, compressing, and expanding before all its parts worked in harmony with one another. Sometimes they never did achieve a Kum Ba Ya moment and the rifle never did shoot well.
Depending on the caliber, how the rifle was bedded, and how good or bad a bedding job it was, this could indeed take months of steady use and a couple of hundred rounds.
However, in the modern era, even inexpensive rifles simply don’t budge. They shoot about the same coming out of the factory box as they do after 15 years and thousands of rounds. The one variable is the barrel, and even that doesn’t vary much. A good barrel is going to shoot well from the first round; a bad barrel will never really shoot well. You may see a little change, but not much.
The only time I’ve seen a miraculous transformation was in a Shaw Rifles .30/06 that I broke in according to Shaw’s formula. According to this procedure, which is a good one and which I still use, you clean the bore after each shot for the first five rounds; then you fire five rounds and clean it; fire ten rounds and clean it; and you’re done.
At the end of the 20 rounds the rifle shot dramatically better than it did when I started. It was like someone had thrown a switch.
This brings us to group testing. According to former Master Gunnery Sergeant Dan Hanus, who was head of the Marine Corps Precision Weapons Section and is now Custom Rifle Production Manager for Bergara Rifles, for an M40-series sniper rifle to pass accuracy standard, it was required to shoot three five-shot groups of less than 3 inches at 300 yards, first unsuppressed, then suppressed.
Since the rifles usually grouped at ½-inch at 100 yards, the Marines would see groups of about 1½ of an inch at 300. There was no break-in period. They shot like that from the get-go or they went back to the shop.
I think this is an extremely sensible way to check the accuracy of a gun that’s going to be used at long range. For the average big-game rifle, which does the vast majority of its shooting at 200 yards or less, a 100-yard check is fine. But for a firearm that’s going to be busy up to 800 yards or farther, 300 yards makes a lot more sense.