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About Corbin Bore Lap Solution

A liquid bore lapping material is available from Corbin in 4-ounce glass bottles, in pint cans, and gallon cans. Corbin Bore Lap is a cream-colored liquid, which is used to polish and lap the gun barrels, and to remove severe fouling and rust, salvaging some guns that would otherwise need to be rebarreled.


Corbin Bore Lap has been available for over 25 years, but the new formulation makes it easier to apply than pastes, and safer to use. Proper procedures include two methods: lead slug lapping, and cloth patch polishing. To use the traditional lead lap, a steel cleaning rod is placed in the barrel, with an appropriate seal (such as a Corbin "Base Guard" copper disk) pushed onto the rod, leaving about an inch of the end projecting past the seal, yet pulled down inside the barrel. Molten lead is then poured into the barrel around this projecting rod end and allowed to cool. The rod is pressed forward, pushing half the length of the lead out the barrel, where a small quantity of Corbin Bore Lap can be applied to it. The rod is the pulled back through the barrel, and half way out the other end, where more lap is applied. The rod is worked back and forth in this way until it becomes loose in the bore. This method can change the finish of the barrel, so it is normally used only on barrels that are not blued yet, or those which will be reblued after the lapping.

A second method for using a lead lap requires a rod with a long threaded end and two compression washers, plus a hollow center core mould (these items can be provided by Corbin on special order). The lead lap is pre-cast in a Corbin mould so it has a hole in the center, and is then placed over the steel lapping rod. The lap is initially a loose fit in the bore. A thin socket wrench is used to tighten a nut and expand the lead slug between two washers once it is pulled into the barrel. This method is only available for larger barrels, since the force required would twist off rods for calibers smaller than .257.

A polishing method which can remove rust, some tool marks and burrs, and severe fouling, uses a brass brush one caliber smaller than the barrel size plus a large cloth patch wrapped around this brush. The bristles force the cloth down into the rifling. A small quantity of Bore Lap is applied to the cloth patch and it is then stroked through the barrel in this way: two inches forward, one inch back, repeated until the patch emerges from the end of the barrel. This method can adversely affect the accuracy of a clean, well-polished barrel, so it should not be used except in an attempt to restore a badly fouled, rusted, or rough barrel. Increases in bore diameter of up to .0015 inches can occur if the process is repeated frequently on the same barrel. Lapping is not a consumer oriented process; professional and responsible amateur gunsmiths are the appropriate clients for using Corbin Bore Lap.

Download the Material Safety Data Sheet for Corbin Bore Lap by selecting the highlighted words in this sentence. The format is Adobe Acrobat PDF. The reader is available free from Adobe systems on their web site.

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