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Fire Lapping a Barrel
by Roy Seifert

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Disclaimer:  This article is for entertainment only and is not to be used in lieu of a qualified gunsmith.  Please defer all firearms work to a qualified gunsmith.  Any loads mentioned in this article are my loads for my guns and have been carefully worked up using established guidelines and special tools.  The author assumes no responsibility or liability for use of these loads, or use or misuse of this article.  Please note that I am not a professional gunsmith, just a shooting enthusiast and hobbyist, as well as a tinkerer.  This article explains work that I performed to my guns without the assistance of a qualified gunsmith.  Some procedures described in this article require special tools and cannot/should not be performed without them.

Warning:  Disassembling and tinkering with your firearm may void the warranty.  I claim no responsibility for use or misuse of this article.  Again, this article is for entertainment purposes only!

Tools and firearms are the trademark/service mark or registered trademark of their respective manufacturers.

Factory rifled barrels are truly a wonder of modern manufacturing.  However, the manufacturing process often leaves the bore rough.  Pits and burrs in the bore, although unseen by the naked eye, can cause the barrel to foul after only a few shots, and can affect accuracy.

There are a number of ways to smooth the bore of a barrel:

  • Shoot the gun a lot – Although this method does work, it is very inconsistent and does not always produce the desired results.
  • Hand lap the barrel – This involves removing the barrel from the receiver, producing a lead lap that fits the bore, impregnating the lap with lapping compound, and moving the impregnated lap through the bore.
  • Polish with a tight patch and fine abrasive compounds – It is possible to polish a barrel using fine abrasive compounds such as Remington Bore Cleaner or USP Bore Paste.  The compound is applied to a tight fitting patch and run back and forth through the bore.  This method works, but takes a very long time to produce any positive results.  (This method can be accelerated with very positive results; see the addendum at the end of this article.)
  • Fire lap the barrel – This is probably the easiest method of all for polishing a bore. 

Fire lapping involves imbedding different grits of lapping compound into bullets and firing them down the barrel at a very moderate velocity.  I use lead bullets for handguns, and copper-jacketed bullets for rifles.  The fire lapping process accomplishes a number of positive things:

  • Smoothes the barrel and removes pits and burrs
  • Removes tight spots
  • Slightly tapers the barrel from forcing cone to muzzle.  This taper keeps the bullet tightly sealed against the lands and grooves as it travels down the bore.

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.

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!


   © Copyright 2009-2011 Roy Seifert.