Gale McMillan, of McMillan Stocks fame, was one of the finest barrel-makers and benchrest shooters of all time. Here he argues that elaborate barrel break-in procedures do more harm than good.
Comments collected from Gale's Gun Forum postings.
As a barrel maker I have looked in thousands of new and used barrels with a bore scope and I will tell you that if every one followed the prescribed [one shot, one clean] break-in method, a very large number would do more harm than good. The reason you hear of the gain in accuracy is because if you chamber a barrel with a reamer that has a dull throater instead of cutting clean sharp rifling it smears a burr up on the down wind side of the rifling. It takes from one to two hundred rounds to burn this burr out and the rifle to settle down and shoot its best. Any one who chambers rifle barrels has tolerances on how dull to let the reamer get and factories let them go longer than any competent smith would.
Another tidbit to consider--take a 300 Win Mag that has a life expectancy of 1000 rounds. Use 10% of it up with your break-in procedure. For every 10 barrels the barrel-maker makes he has to make one more just to take care of the break-in. No wonder barrel-makers like to see this. Now when you flame me on this please [explain] what you think is happening to the inside of your barrel during the break in that is helping you.
Consider this: every round shot in breaking-in a barrel is one round off the life of said rifle barrel. No one has ever told me the physical reason of what happens during break-in firing. In other words what, to the number of pounds of powder shot at any given pressure, is the life of the barrel. No one has ever explained what is being accomplished by shooting and cleaning in any prescribed method. Start your barrel off with 5 rounds and clean it thoroughly and do it again. Nev Maden, a friend down under that my brother taught to make barrels was the one who came up with the [one shot one clean] break-in method. He may think he has come upon something, or he has come up with another way to sell barrels. I feel that the first shot out of a barrel is its best and every one after that deteriorates [the bore] until the barrel is gone. If some one can explain what physically takes place during break-in to modify the barrel then I may change my mind. As the physical properties of a barrel don't change because of the break-in procedures it means it's all hog wash. I am open to any suggestions that can be documented otherwise if it is just someone's opinion--forget it.
It all got started when a barrel maker that I know started putting break-in instructions in the box with each barrel he shipped a few years ago. I asked him how he figured it would help and his reply was if they shoot 100 rounds breaking in this barrel that's total life is 3000 rounds and I make 1000 barrels a year just figure how many more barrels I will get to make. He had a point; it definately will shorten the barrel life. I have been a barrel maker a fair amount of time and my barrels have set and reset benchrest world records so many times I quit keeping track (at one time they held 7 at one time) along with High Power, Silhouette, Smallbore national and world records and my instructions were to clean as often as possible preferably every 10 rounds. I inspect every barrel taken off and every new barrel before it is shipped with a bore scope and I will tell you all that I see far more barrels ruined by cleaning rods than I see worn out from normal wear and tear. I am even reading about people recommending breaking-in pistols. As if it will help their shooting ability or the guns'.
More from Gale McMillan: http://www.snipercountry.com/Articles/Barrel_BreakIn.asp