Leade Lapping A Bore For More Efficient Barrel Break In

A key area of concern in barrel break-in involves the throat or leade of the bore where the lands begin. As put by Krieger Barrels—a manufacturer of some of the world’s best barrels—the throat or leade of a barrel is of major concern during the break-in period. Here is the company’s synopsis. "With any barrel that has been lapped, the lay or direction of the finish follows bullet travel.

Because the lay of the finish is in the direction of bullet travel, very little is done to the bore during break-in … but the throat is another story. As the barrel is chambered there are reamer marks left in the throat that are across the lands, much like the teeth on a very fine fi le. When the bullet is forced into the throat or leade, copper dust is released into the gas, which at this temperature and pressure is actually a plasma. The copper dust is vaporized and carried down the barrel.

As the gas expands and cools, the copper comes out of suspension and is deposited in the bore. This makes it appear as if the source of the fouling is the bore when it is actually, for the most part, the new throat. If the copper is allowed to stay in the bore and subsequent bullets and deposits are fi red over it—copper, which adheres well to itself will build up quickly and may be difficult to remove later. So when we break in a barrel, our Much of this copper adheres to the bore during the break-in period.

Leade-lapping, as described in text, can appreciably cut the follow-up, shoot-clean phase of bore break-in. goal is to get the throat polished without allowing copper to build up in the bore. This is the reasoning behind the shoot-and-clean procedure. The goal is to get and keep the barrel clean while polishing out the throat." With this in mind, I have developed a procedure to hasten barrel break-in that is quick and easy to perform.

I simply micro-lap the throat section with snug fitting patches cut from abrasive sheet material made by 3M The 3M lapping paper is coated with micron-graded mineral patches on a high strength polyester backing. The available mineral abrasives are aluminum oxide or silicone carbide in micron grades 1, 2, 3, 9, 15 and 30. These numbers correspond to US mesh grades 8000, 6000, 4000, 1200, 600 and 400, respectively.

Here I simply cut small patches of the 600 or 400 mesh grade paper to fit the bore size I am working with. These polishing patches are backed by a common cleaning patch and pushed snugly into the throat,

using a proper size cleaning rod jag. It is important that these double patches fit the throat very firmly and the cleaning rod is perfectly in line with the bore. I usually have the barrel in a padded vise for this procedure. If the barrel remains on the action I use a cleaning rod guide. With a snugly fitting patch, a throat can be properly polished in as few as a dozen inch-long strokes using either 400 or 600 mesh grade paper. A good bore scope is helpful to monitor the throat as you lap the leade.

You will be amazed how effi ciently this lapping is performed. This will hasten the remaining bore break-in requiring far fewer shots than are commonly used with the shoot-clean method. Muzzle Collects Copper First During the final bore break-in, the commonly shoot-clean method is used. Ordinarily, the customer does this and should be instructed on proper procedure. While barrels break in differently, cleaning the bore after each shot for the first fi ve to ten rounds is recommended.

Cleaning after each fi ve shots thereafter until the bore no longer collects copper is the follow-up procedure. Copper will invariably collect near the muzzle of a barrel and a ten minute soak in the forward bore with a strong bore-cleaner like Barnes CR- 10, Ventco Industries Copper Remover or Montana Extreme’s Copper Killer does a good job of removing it. A good From left, a square piece of 3-M, 400 mesh grade silicon carbide lapping paper over a common cleaning patch as used to lap the leade (throat) of a bore.

The center patch has been used to lap the leade and the patch on jag shows how the pressure of the bore forms the patch to a tightly fitted lap. bore scope will help in monitoring progress during the fi nal shoot-clean process. rifle accuracy and help from the gunsmith is a good place to begin. Offering this service along with good information makes your shop a better one to come to.

AG Bore break-in is a very critical area in attaining the best possible It is at this area where lapping smooths out the roughness left by the reamer as a means of reducing the commonly used shoot-clean method.