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I purchased a fire-lapping kit from NECO, which included 4 grits of lapping compound, 220, 400, 800, and 1200.  Their instruction manual said to use lead bullets to fire-lap a revolver barrel, and shoot multiple exact full cylinders of bullets.  (This is so each chamber throat in the cylinder gets the same amount of polishing.)  They recommended 12 rounds with 220 grit, 18 rounds with 400 grit, and 24 rounds with 800 grit.  They did not recommend using the 1200 grit but they stated it couldn’t hurt. 

For rifle barrels, they recommend firing five rounds of each grit, cleaning the barrel, then slugging it to gauge the progress.  I prefer NECO’s other recommendation of shooting ten rounds of each grit and cleaning the barrel after every five rounds.  It is important to thoroughly clean a revolver barrel after every full cylinder of shots, and to clean a rifle barrel after every five shots to remove the powder residue and fouling.  Otherwise, I would be lapping the fouling and not the barrel.

I spread a thin layer of compound on the steel plate provided in the NECO kit and rolled three bullets at a time between it and another steel plate thereby impregnating the bullets.  I wiped off the excess compound from each bullet and separated them by grit in preparation for loading.  

A properly impregnated bullet has a gray ring around the bearing surface.  This surface provides the lapping action as the bullet travels down the bore.  I loaded each round with a light load of Red Dot, which produced a low velocity load.  I normally destroy the cases after using them for fire lapping.  If I was to reload these cases, residual lapping compound could contaminate the bullet, which would damage the barrel.  However, because I plan to fire lap more then one gun of the same caliber, I can re-use the cases, but I have to keep them separated by grit.

Ok, off to the range.  As mentioned before, I need to thoroughly clean the barrel after every full cylinder for a revolver, and after every five shots with a rifle.

So, what about the results, and just how effective is fire lapping for improving accuracy?  First of all, a fire lapped barrel is much easier to clean.  Because pits and burrs are removed, there is nothing to hold fouling.  In most cases, a fire lapped barrel will come clean after only two or three solvent-soaked patches.

I have a Chinese Polytech M1A with which I could barely keep the shots in a six-inch dinner plate at 100 yards.  I figured the barrel was rough built and could probably be improved by fire lapping.  After fire lapping the barrel and cleaning up the muzzle with a brass muzzle lap, I was consistently shooting 2-inch walnut husks at 100 yards.  On paper, I was printing sub minute-of-angle groups.  “Your results may vary”, as the disclaimers say, but I was quite stunned by the results.

I would not fire lap a custom-made barrel because those are usually hand-lapped at the factory.  NECO recommends that the 220-grit lapping compound should not be used in good quality factory barrels.  I did use the 220-grit on my Chinese M1A barrel because I could see it was very rough inside.

I do not fire lap every gun I own because most of them shoot great right out of the box.  However, if I have a revolver that has a constriction in the barrel where it is screwed into the frame, or a poor-quality barrel, I will fire lap it.  Fire lapping will NOT restore a worn or shot-out barrel such as you might find on a military surplus weapon, and it may not improve the accuracy of an already accurate barrel, but it will make the bore smoother and easier to clean.

Addendum
I found an interesting article online at the Twin City Rod and Gun web site that provided a process for hand-lapping a barrel using three different grits of cleaning compound and tight patches. Fire-lapping involves shooting a bullet impregnated with lapping compound down the bore at a much reduced velocity and pressure. This has the effect of both polishing and tapering the bore for maximum accuracy, but it can also open and lengthen the throat. I found an article on the Los Angeles Silhouette Club web site written by Ken Mollohan that has a little different method for fire-lapping. Ken first ran a bore mop impregnated with J-B® Bore Cleaning Compound through the bore being careful not to get any compound in the chamber, then fired a low velocity, low pressure jacketed round through the bore. He repeated this process 5 or 6 times, then thoroughly cleaned the barrel. This process not only provided all the benefits of fire-lapping, but it prevented damage to the throat, and since the bullet itself was not impregnated with the lapping compound, the cartridge cases did not have to be thrown away.

I decided to try a combination of both methods on a new M1 Garand barrel. First I loaded 10 rounds of .30-06 with 5.0 grains of Red Dot behind a 150 grain FMJ boat tail .308 bullet and a large rifle magnum primer. I put an empty case in the chamber and closed the bolt to prevent compound from getting into the chamber, impregnated a bore mop with USP Bore Paste, then ran the mop back and forth through the entire length of the bore 20 times. This left a small amount of compound in the bore. I fired one low velocity round through the barrel, inserted the same empty case into the chamber that I had used before, then again ran the impregnated bore mop back and forth through the bore several times. This cleaned any powder residue and fouling from the bore and prepared it for a second shot. After performing this for 5 shots, I thoroughly cleaned the barrel using solvent and dry patches.

I threw away the first empty case I used and put a new empty case in the chamber and closed the bolt. I impregnated a clean bore mop with J-B® Bore Bright which has a finer grit and ran the mop back and forth through the entire length of the bore 20 times. I fired one low velocity round through the barrel, inserted the same empty case into the chamber, then again ran the impregnated bore mop back and forth through the bore several times. This again cleaned any powder residue and fouling from the bore and prepared it for a second shot. After performing this for 5 shots, I thoroughly cleaned the barrel using solvent and dry patches. The bore was mirror bright and smooth and was now ready for full pressure loads, and in theory the new throat was polished which should help to prevent excessive fouling.

The advantages of using this method are that the chamber throat is not excessively lengthened due to using rougher grit, and the cartridge cases can be reused for normal loads.  As for the results, I fired maybe 60 rounds through the new barrel and it cleaned up with only three patches and I had no copper fouling.  Now that's success!