FIRE LAPPING a Bad or Fouled Rifle Barrel



 Inaccurate Rifle  ?   Do you have a rifle sitting in your gun vault that you have not shot for a while because it is inaccurate?  You cleaned the bore numerous times.  Maybe you have tried different reloads thinking you had not found the right one that it liked?  Is the scope mount loose?  You might even have tried a different scope on it, just to see if the old one was faulty?   You have rebedded it and free floated the barrel, but still nothing seems to help.  You even re-crowned the muzzle and adjusted the trigger pull to a more reasonable let off.  There are many things to look for in these situations and you probably have already covered most all of them, before you kind of gave up and parked it until your blood pressure cooled down.


 Did You Really Clean the Bore  ?   Many times looking down the bore, or even running a cleaning patch through it does not really tell the whole story.  Look REAL close for copper fouling in the bore.  Sometimes it is even prevalent at the muzzle and is obvious.  In today's world you will probably not see lead fouling, but more than likely copper, since many of the modern bullets have slid into being made softer to control expansion.  This however can have side effects.

There are a few methods of dealing with this, (1) being scrubbing it with a bore cleaner.   Many times this stuff will contain Ammonia, which is obvious when you open the bottle cap.   Some instructions say to swab it with a saturated loose patch, allowing it to set for a prescribed time, then do it again, and again.  Then use a oversized nylon brush to clean the gunk out, run a clean patch through it and hope it is now clean.  Well maybe.  You might have to do this NUMEROUS times to achieve your goal if the fouling is bad.

(2) Another method is the Outers Foul Out system.  This system can be used on a gun without removing the stock.  First the bore needs to be cleaned of any oil.  This system consists of a bottle of solution, either for lead, or another for copper where you plug the chamber with a tapered rubber plug.   A small stainless steel rod is used down the bore that is insulated from the inner bore by a couple of Neoprene O-Rings (lower and upper) and filling the bore with the appropriate solution.  Then connect the electric control box with one cable to a metal part on the receiver, (even trigger guard) and the other clamp on the rod protruding out the muzzle.  Turn the machine on and wait the prescribed amount of time.  Turn it off and pull the rod out.  If there is any copper imbedded in the bore, it will be transferred to this stainless steel rod.  Use fine steel wool to remove this residue and start over if needed.  Repeat until the rod does not accumulate any more residue.

Usually the above will methods will make a big difference it that is the problem.  But what if the problem initially was a rough bore, either because of rust or from the factory putting out a rough bore.  Neither of the above methods will cure this situation, but would prepare the gun for #3.  But without expensive sophisticated equipment, you can not look inside the bore to really tell.  And what caused the fouling to start with?  There usually had to be something that caused this copper transfer, which just keeps getting worse if not corrected.

I like to do either of the above and then in addition (3)  There might be a few different names attached to this method (depending on who is promoting it) but it is called Fire Lapping by most gun enthusiasts and gunsmiths.  In essence, you imbed a lead bullet of the right caliber with abrasive valve grinding compound, load this bullet over a pistol charge and shoot it out the bore.

Shown in the photo below is part of the procedure.   Cast up about 20 lead bullets matching the caliber of the gun.   I do not size them (but shoot as cast) as being lead and oversize has it's benefits here.    Use both Medium grit and fine grit valve grinding compound.  Select a piece of scrap window glass and a bar of flat steel approx. 5/16" thick X 1 1/2" X 6" long.  Smear the medium grit on the glass, lay about 10 bullets on this grit, smear more on top of the bullets, lay the steel plate on top of the bullets and press down hard along with a forward /aft motion, rolling the bullets into the compound.  You may want to smear more compound and do it again a few times.  Your objective is to IMBED this grit INTO the outer edges of the lead bullet.


Resize your cartridge case and prime it.  You may also want to flare the case neck mouth slightly so the bullet will enter without shaving the grit off, but not enough to interfere with loading into the chamber.  This can be done with a neck expander, set so it just SLIGHTLY flares the end.  If you do not have access to a neck expander, you may get by with using a hand chamfering tool and slightly bevel the inside of the case neck, eliminating any sharp edge.  The bullets used here were designed for gas checks, but I did not install them, as the smaller diameter at the base without the gas checks allowed the slightly oversize (as cast) bullet to be seated easier.


Load the case with about 5 grains of Unique pistol powder.  All you really want is to push the bullet out the bore with enough force to not get it stuck (basically a pistol load).  On top of this powder charge, tamp in a small 1" square section of toilet tissue, Kleenex, or paper towel.  This readily burnable paper is simply to hold the powder at the rear against the powder since it is such a small charge in a large case.  This is common practice on reduced lead loads, as loads like this have been known to create excessive pressure if the primer flashes over the whole length of powder in the case if the gun held down or horizontal.  It needs to burn at a progressive rate instead of instantaneously. 


Seat your bullet, wipe of any excess grit off the case neck and bullet, and go out firing your 10 rounds.  I say 10, as that is the quantity that I have found works quite well.


After firing, clean the chamber and bore.  Repeat the above procedure, but this time go to the finer grit for your last round of lapping.


Again clean the chamber and bore of any grit/residue left.  Run a new patch through the bore.  It will usually come out dark the first couple of times, but cleans up after a few more.  As a final, run another couple of patches, but oily ones this time to protect the now clean bore.


Here you see my "KIT"


The rifle/caliber here was a custom 98 Mauser lightweight 7mm-08  that had a Shilen premium barrel, that over the years accuracy had deteriorated.  He used to be able to hold a 1" group, but lately it stretched to 3".  This owner is more than just a average shooter, but did not understand, or realize the problems that had occurred.   He was to the point of thinking about installing a new barrel, thinking that the existing one may have been too light a weight.


Here you can see the grit on the unseated bullet


7 X 30 Waters ;  Next on my list is a scope mounted 7X30 Waters carbine barrel for a Thompson Contender, that even right out of the box was so inaccurate that before the first box of ammo was fired out of it, that it just sat in a vault for 20 years.  


Well, I did my normal Fire Lapping job and in the final cleaning process, looking down the bore, did not like what I saw.  There was numerous black spots near the chamber end for about 4".    In my old gunsmithing years, I even owned a rebore and rifling machine.  In conjunction with this, I also owned a special bore inspection light/probe, (that I kept when I sold the rebore machine) and in using it here, what I saw was that this barrel would be classified as a REJECT if it was one I was rifling.  Numerous places along the whole rear section where gouges of metal torn out, indicative of dull cutters or lack of lubricant and/or shoddy workmanship.  And to make matters worse, it uses an 8 groove 1 in 9 rifling that has equal spaced lands/grooves.  Under this rough condition, to me, it does not give the bullet enough of a chance to grip the bullet, and woe is the guy who may try to use cast bullets in it (which was my intention).


With the factory discontinuing this model years ago, there is no chance of returning it to the factory.   So I guess this will give me a chance to really prove whether this Fire Lapping can be effective.  I will have to make a trip to the range and see if this first go around did anything.  If not, then it looks like I will try another round of Fire Lapping, but will get aggressive and run possibly 40 rounds (OR MORE) of the courser grit to start with.   It is so bad now that even if I happen to get it a smidgen oversize, accuracy can not get any worse.


A Few More to Look At ;    Then a Remington model 760 that was rebarreled from 30-06 to 25-06.   Following that will be a Savage model 2400 O/U 12 ga. over a  rebarreled from 222 Rem. to 270 Win.    These had new barrels installed and have been sitting for YEARS because of inaccuracy.   Now that I have retired from gunsmithing, I am trying to clean up stuff that has been sitting in the vault for too long.


The Old Way ;  In years past, bore lapping was done by hand, by running a ramrod with a really demolished brass brush (to hold the lead) up the bore from the breech.  Wrap a small amount of cleaning batch the rear of this brush and push it up to where the brush tip was about 1/2" below the muzzle.  Heat up some lead and pour into the muzzle.  If it ran over at the muzzle, push the ramrod so the lead was slightly exposed, and with your knife, cut off any excess.  Carefully push the lead out of the muzzle, BUT NOT ENOUGH TO DISENGAGE THE RIFLING.  Smear medium valve grinding compound on this lap, and get busy pushing and pulling it from one end to the other, being careful to not go all the way out.    If you do, you will have to CAREFULLY realign the lap to the correct rifling it came out of.


Here you push/pull until the resistance has diminished, push the lap partly out again and smear more compound.  Repeat this procedure until your arms get tired.   You can recast another lap OR with the lap just inside the muzzle, with a brass rod that has a squared off end, poke in in on top of the lap and rap it hard with a hammer, expanding it.  Do your push/pull thing again.  This method has been used for years, but is time consuming.  Fire lapping just as effective, OR MORESO and it is a lot faster.  


Previous Usage That Convinced Me ;   This Fire Lapping was not my idea, and has been around for at least 20 years.  My introduction to it was when I owned and was running a full time gunsmithing shop that included being a regional warranty repair center for 8 major firearms companies.   Through advertising, I read about Fire Lapping being offered in a Kit Form, but the process was being kept pretty mum.  After studying the what the advertisers listed, I simply applied the method using my existing material. 


Of the gun manufacturers that I was warranty for, only one was prone to inaccuracy with complaining customers.  This was Weatherby.  Now as a warranty center, we were bound to what the factory would allow us to do.  Their guarantee was  (1) group size was guaranteed to be no more than 2" at 100 yards.  (2) There HAD TO BE STOCK PRESSUE from the forearm to the barrel of 6#-8#.  Which meant NO FREE FLOATING, otherwise we voided the customer's warranty. 


Two inch group ??   Most modern rifles will produce closer to 1" or less.  Forend pressure ??  This may have been OK in dry climates like the southern SW, but here in Washington State, no matter how well the stock is sealed (unless it is synthetic), and with Weatherby trying to use a more fancy wood, these stocks do warp.  


Their factory ammo is pushing bullets FASTER than most, along with the use of SOFTER COPPER bullet jackets, give you a combination of copper fouling of barrels IF the bore was even somewhat rough to start with.   After looking at the insides many of these bores, it became obvious that the problem of a 6" or even 8" group was bore fouling.  Initially the factory insisted that it was the customer's responsibility to maintain their bore cleanliness.  But it was the factory who may have put out a slightly rough bore and sold the customer the soft jacketed bullet.  After lots of conversation, I finally got permission from the service manager of Weatherby to Fire Lap their bores on these types of repairs.  PROBLEM SOLVED, and we never had those rifles be returned for the same problem.


On these rifles, I initially did the Outers Foul-Out for a day (which was the least labor intensive in our shop) and then the Fire Lapping.   This is where I decided 10 rounds of each grit was working.  Why do less as it takes only a few more minutes to do 10 as 5?  And the cleanup time is the same. 



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Originated 01-04-2017, Last updated 04-08-2017
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