With articles by Ken Mollohan, John
Robinson and John Cox
In 1994 I tested a New England Firearms
Handi-Rifle in 30/30, and wrote an article about that test for the ASSRA
News. In the article was mention of how Lindy Blaisdell claimed to have
shot bullets coated with J-B Bore Cleaner through his de Haas
Miller/Douglas bench rifle and made it into the match winner it is today.
We’ve never known whether to believe that story of Lindy’s-he’s known for
his fish stories.
After the article was published I got a
letter from Roger Johnston at NECO (Nostalgia Enterprises Co., 1316-67th
Street, Emeryville CA 94608) informing me that they were in the business
of making and selling “Pressure (Fire) Lapping” materials and kits. Fire
Lapping is a process of shooting abrasive coated bullets through a rifle
barrel, with the goal of improving accuracy.
I wrote NECO asking for a sample kit to
test, and wrote New England Firearms asking for another Handi-Rifle in
30/30 to test. Robin Sharpless at New England Firearms was extremely
cooperative, and sent me a rifle that I received in February of 1995.
Roger Johnston sent me a Pressure (Fire) Lapping kit with a manual.
The first time at the range with the
rifle it shot a 15/16” group, and averaged 1 7/16” for five, five shot
groups at 100 yards. It never shot as well through June of 1995, averaging
around 2” for my standard set of five groups of five shots each at 100
yards. The rifle did not shoot another one inch or smaller group from
February through June. I fired about 400 shots with the rifle in this time
The recipe was the Lyman 311299 sized
in an oversize .312 die and lubricated with Alox, IMR 4227 powder in
charges from 13 to 14.5 grains, Remington #2 1/2 Large Pistol Primers, and
either fixed ammunition or the bullet seated in the reloaded case by hand
or the bullet just barely breech - seated with a pen.
There didn’t seem to be any improvement
in the group size as I varied powder charge and loading method, so it was
time to Fire Lap.
I attempted to follow the instructions
in the Fire Lapping Manual, but was not successful in “feeling” the
variation in the bore of the rifle as a bullet was pushed back and forth
in the bore. The instructions in the manual are complex but vague, in that
the decisions about how and how much Fire Lapping is to be done are left
to the reader, and these decisions are based on slugging the bore and
pushing the slug around in the bore and measuring at various points and
feeling tight and loose spots. I guess that I just don’t have a feel for
that sort of measurement-I concluded that the bore on the Handi-Rifle was
uniform and without tight or loose spots.
The kit had four containers of
abrasive, in #220 (Coarse), #400 (Medium), #800 (Fine) and #1200 (Polish)
grits. It also had two steel plates. The abrasive is spread onto the
larger plate, and the bullet is rolled with the smaller plate, embedding
the abrasive into the bullets. The two - diameter bullets used had the
abrasive embedded into the base band and the front, bore-riding area. I
prepared five cartridges using each of the four grits of abrasive (a total
of 20 cartridges), with soft commercially cast bullets similar to the
Lyman 31141, 10 grains of Unique, and Remington 2 1/2 primers. Embedding
the grit into the bullets and loading the cartridges was a messy business,
the abrasive spreads magically, and must be cleaned off of everything,
including the inside of the seating die.
I cleaned the rifle, shot the #220 grit
coated bullets, cleaned the rifle, shot the #400 grit coated bullets, and
so on through the four grits. Following directions, I threw away the
cartridge cases after firing them. The bore leaded slightly during each
set of five shots.
On the 25th of June I shot one group of
15/16”, and an average for five, five shot groups of 1 3/4”. There was
vertical stringing, so on the second of July I increased the powder charge
by half a grain, and shot groups of 7/8” and 1”, and an average of 1 5/32
for five, five shot groups. The loading method for this last target was to
slightly breech - seat the bullet in the chamber with a pen - the charge
was 14 grains of IMR 4227.
The February 18th target was shot with
a 3-9X Weaver scope, all other targets were shot with a 24X Redfield 3200
that I borrowed from George Badgio.
The rifle has a very heavy trigger
pull, my guess is 10 pounds or more.
Did the Pressure (Fire) Lapping work?
It looks to me as though it did. The
convincer for me was the two groups under an inch and one at one inch, out
of the 10 groups shot after fire lapping. I had not been able to shoot a
one inch group with the rifle from February to June.
How To Fire Lap
First let me confess that I’ve never
tried any of the recommended procedures for ‘conventional’ fire lapping.
I’ve given it some thought, but the idea of pouring coarse abrasives down
the bore of a fine rifle just gave me the galloping willies. And when
reports started filtering back in that some of these kits caused
substantial throat and leade enlargements, I turned thumbs down on using
them in any of MY rifles, interesting as the concept might be. I’d use
hand lapping, if I had to use any at all.
But one day I picked up a brand new
rifle, and after I cleaned the Cosmoline out, I found it had a roughly
finished bore. I still thought the idea of rough abrasives was
unattractive, but I began to wonder if a very fine abrasive might be less
To make a long story shorter, I worked
out a procedure that I thought offered a good chance of smoothing the bore
with a minimal chance of ruining it. It’s a quick and easy bore
clean/polish technique that has worked very well for me, and for a few
others too. It was written up in the CBA's 'Fouling Shot' magazine, but
here's the short version:
Take everything to the range, and
proceed as follows:
1. Remove the bolt from the rifle.
2. Coat the bore mop lightly with JB
3. Swab the bore
several times to leave a LIGHT coating of JB compound throughout.
4. Replace the bolt.
5. Load with special ammo and fire.
6. Remove the bolt, swab the bore and
repeat for about half a dozen rounds.
7. Clean the bore to check on
8. Repeat as necessary.
1. Used with some common sense, this process
works beautifully and quickly: It will leave a bore mirror bright if
everything is done correctly, but will result in little or no enlargement.
But it CAN be hazardous if the following warnings are not carefully
2. You MUST NOT use factory ammo or handloads
that even come close to factory pressures. This procedure will elevate
pressures, and if factory ammo is used, the results could be very
dangerous. The reason is at least two-fold:
The JB compound will increase the
friction between the barrel and the bullet quite a bit, requiring much
higher pressures to push the bullet down the bore.
Also, the paste will reduce the
clearance at the case neck. If
the chamber neck area is
too heavily coated with JB compound, the case won't be able to expand and
release the bullet easily. This can also raise pressures quite a bit. And
a heavy coating of JB compound won't work any better or faster than a thin
coating, so use some common sense.
I found that removing at least 1/3 of
the powder charge from a round of factory jacketed ammo seemed to give
very satisfactory results. But I will probably use a 50% powder charge
(for an extra safety
margin) the next time I try this.
3. I used jacketed bullets for this
lapping/polishing and got fine results. A new rifle with an obviously
rough bore gleamed like chrome after about five or six shots. A pitted
bore will undoubtedly require more shots.
I strongly suspect that if you want to
use cast bullets for this lapping, you may
get somewhat slower but still safer results.
4. Cast bullets may have another advantage
too: Cast bullets will expand much more easily, and fill the bore grooves
for more uniform polishing. Jacketed bullets may not fill the groove
corners quite so well.
5. As an extra safety margin, I recommend
firing the rifle from the bench (not the shoulder) with the bolt and
breech covered with a couple of sandbags. I think this should be adequate
to provide greatly improved safety even is everything else goes wrong.
Sorry about all the potential hazard
warnings, but they ARE just potential - not necessarily probable -
hazards. I think the process is plenty safe if used by someone with
ordinary experience and caution, but I have no way of knowing your
experience or the level of caution you consider appropriate. So this
information is for your information and consideration only; it is not a
recommendation to be implemented blindly. Use at your own judgment and
"I have cured several chronic leaders
(Sixguns) without resorting to lapping of any kind.
I started with a K-38 that just
wouldn't respond to any traditional ways of jacking with alloys, pressure,
and lube to cure the leading. I was about ready to trade it off, but just
could not bring my self to do so. Until
the lead built up, it was so accurate it was scary. The barrel was just
rough with machine hickies. You couldn't see them, but they had to be
I loaded 200 rounds of jacketed bullets
at full snort pressure and fired them as fast as I could load and shoot.
No attempt was made to hit anything. I then dropped the cylinder out, and
wearing gloves (the pistol was HOT), I took a new bronze brush and
Shooters choice and gave the barrel 200 fore and after stroked.
Back at the house, I used a tight patch
and some JB Paste to remove any metal fouling remaining and there was
I then used very tight patches and
Semi-Chrome metal polish and worked on the bore for at least a half hour.
I did it until my arms felt like they were going to fall off
A clean up and that was that. The bore
is mirror bright and just won't lead. It is also very easy and quick to
clean. Accuracy if anything was improved a mite.
Talk about your constrictions where the
barrel screwed into the frame? They were there and as easy to see as a rat
turd in the sugar bowl. However, they did no harm at all. The bullet has
plenty of time to recover from any damage after the pass over that short
stretch of the barrel. It is for this reason, I doubt the so called
negative effects of frame/barrel constrictions in Sixguns. I have done
this on 15 to 20 other Sixguns and the results are always the same. The
leading stops, the accuracy picks up, and the constrictions are still
there and very evident. There are no changes in handgun dimensions like
there is when a barrel is lapped.
I did not invent the above method, but
read it in some gun magazine, but I don't remember which, when and who
revolver frame/barrel constriction out.)
"Not too complicated. Use a one piece
steel cleaning rod with a cleaning jag a bit too small for the bore. Use a
couple patches made of some soft material, like an old tee shirt, to make
some padding. Use a strong material to make the patch that holds the
lapping compound, like the legs from an old pair of blue jeans.
Start with a pretty rough grit of
lapping compound, like 220 or 260. Impregnate the blue jean patch with the
compound, put it over the 'padding' patches, and force it into the bore.
It needs to be a very tight, compressed fit. Don't lap much on spots that
aren't constricted (you can feel it where the barrel tightens up). Work
the tight spots well until you feel them loosen up some. As you push the
rod back and forth, vary the length of strokes so you don't wear a
circular groove in the same place in the barrel. Quit as soon as you feel
it opening the constriction(s).
Clean out the barrel. Replace the
patches and repeat with a finer lapping compound, like 320 or so. Then
again with 400 grit. Beyond 400, you're probably reaching the point of
diminishing returns. With the last grit you use, be sure to "feather" the
laps and then make several (say, 10-20) full length strokes so the entire
barrel is uniformly lapped. Pay special attention to the smoothness of the
strokes; you can feel any roughness or tight spots.
Clean everything up and inspect it
under a bright light to make sure you haven't missed anything. You're
ready to shoot."
GRUMBLE on cast boolits
Fire Lapping once had a mystique that
drastic improvements in accuracy could be obtained. Since its wide spread
use, we have learned that it can be damaging too if improperly done. This
is not to debate its merits or short comings, only to inform you enough to
understand the process and how I have developed a technique that works for
me. This is not all-inclusive because I am still learning.
Fire lapping involves the loading and
firing of any material slug loaded or rolled in an abrasive compound.
Directions for this procedure come with every kit purchased. To load these
bullets requires some ingenious method to remove a spent primer from a
case without sizing it. We don’t want sized cases or lap compound in our
dies. I remove and use the de-priming stem from my die. Then I re-prime
and charge with powder and insert the bullet by hand. If the case is too
loose, then partially size it on a trial and error basis until enough
tension can be maintained that the bullet doesn’t fall back into the case.
Seat deep enough to just clear the lands to cut pressure. What else is
needed is a complete understanding of how to slug your throats and measure
slugs. This is your quality control tool to prevent you from doing too
much damage to your gun. Ignore this step at your own peril. I have
successfully lapped over 70 barrels for both rifles and handguns
butchering a couple in the process. What you should get out of this
article is the benefit of my knowledge to this point.
Many ask themselves, mostly out of fear
of the process, if they should fire lap. The correct way to look at fire
lapping is that you do it all the time with every shot you put down the
bore. All you simply have to decide is if you need any additives to
expedite the process. Then you must be able to understand the process
fully. Understanding brings the ability to “think” about what actually
“needs” to be done. It also helps to have realistic expectations about the
process. Another point important to understand is that barrel accuracy
goes beyond dimensional perfection. In other words, just because you
remove whatever problem was causing you to copper / lead, doesn’t mean
accuracy is necessarily going to improve. So you don’t have to reach
perfection either. Take a moment to think about this paragraph for a
minute. Read it again if you have to and the rest of this will make sense.
If I haven’t lost you, let me give you
an example. A hand gunner that shoots soft lead, plain-based bullets isn’t
going to notice a constriction in his forcing cone as much as a hard
caster will. This is because it will be easier for the plain base,
soft caster to find loads that obturate the bullet a second time once it
has passed the constriction in the forcing cone. Say both of these guys
decide to fire lap. Assuming they have done it properly, the soft guy says
he sees no improvement at all. The hard guy says wow no leading! The first
guy expected an accuracy improvement. And maybe he got some, just not
enough to justify his efforts / risks. The hard cast guy understands that
now his odds for accuracy increase if he is not leading any more. If they
both thought groups were going to magically drop to 1” at 25 yards with
every bullet / load, they are both disappointed. The key here is
results depend on whom you talk to and if it solved a problem for them or
Dimensional perfection and surface
finish cause bore resistance in the form of friction. Friction affects
harmonic resonance, and possibly ignition factors too if conditions are
bad enough. If you change those conditions, understand that it is very
likely the lap process will alter the accuracy of your existing loads.
You can’t simply do a before and after test and draw any reliable
conclusions without further load adjustment to get back to the harmonic
So maybe it would help if you
understood more about the process. If you want a guarantee or cutting
chart stop reading now, you are wasting your time. If your question is how
much metal will be removed if I use 50 rounds of 220 grit? The answer is
maybe none where you want it removed. On the other hand, you could be
using 400 grit and have 50 shots cut way too much. The reason for this is
the same as with everything else in shooting, variables. Bullet hardness
affects cutting rate. So does the type of the steel. Stainless cuts faster
than chrome moly. So does the existing throat angle, bore finish, and
diameter. So does your chosen powder speed and pressure level.
If you have more resistance to a bullet going down your bore, you are
going to throw more pressure than someone who doesn’t. The more pressure
means more obturation, and thus a greater cutting force. In this case,
you definitely don’t want to be a choker with lead.
The good news is that there are
products out on the market like the Tubb’s Bore Polishing System that use
jacketed and will remove virtually nothing if you follow the instructions.
They are designed to only improve internal finish without changing
dimensions. The manufacturer claims .0003. I can’t measure any difference
after use with my mics on a slug, so I would say that is realistic. That
is three tenths of .001. Pretty small. Does it work? Yes and no.
Here is an example. An air gauged, hand
lapped, 7X57AI barrel had over 200 rounds through it following the
manufacturers break in procedure to the letter. After those 200 rounds the
first three shots from a perfectly clean barrel went into 1 ¼”. The next
three were 2 ½”. The third three went to 4” plus and you looked like you
owned a gold mine if you looked in the muzzle. Shooting lead was limited
to hard bullets at modest cast velocities. The Tubb’s kit was shot through
the gun following the instructions supplied with the product requiring you
to fire up to 50 shots.
Before I started, I set up the seating
die to moderately engrave a jacketed bullet. This was to monitor minimal
amounts of throat wear after each ten shots and eliminate the need to
slug. I had to use all 50 shots for this rough surfaced barrel. After
completion, with the same brand of ammunition, the first three shots still
shoot 1 ¼”. The next three shots are 1 ¼”. And the third three hold at 1
5/8”. I can still see copper starting to build on the drive side of the
lands at the muzzle. But this is a major improvement. So this barrel
could benefit from even more shots. But since this is a 5 lb rifle, it is
fine for hunting at this point. At least you can now do “reliable” load
development without cleaning all the time. This barrel still fouls to the
point that accuracy is affected sooner than “I” would prefer for my own
rifle. I want a minimum of 20 rounds before cleaning is required. Now if
my goals were not to copper at all, (unrealistic) I would be disappointed
in the product’s performance on this barrel. If I expected a big pick up
in accuracy, I would be disappointed also.
If you simply want to fire lap to
remove the sharp edges due to tool marks and are worried about removing
too much metal, then the Tubb’s system is an excellent, idiot proof setup,
if you follow the instructions. What happens if you run them too fast? I
don’t know because I follow the instructions. If you call the company,
they will help with load data. Checking the throat of this gun today has
rifling contact begins on the ogive where it did before this test, but the
contact mark is shorter and lighter than before. In short, the diameter
changed very little and the throat angle did moderate only slightly. Just
not enough to change my dies. If you have a bore that is in fairly good
condition, meaning it takes about 20 rounds before shooting causes
accuracy loss, then this product is for you. It will almost stop coppering
or leading beyond the throat based upon my testing. It speeds the cleaning
process from 6 hours to 15 minutes on this rifle mentioned regardless of
any other positives you will receive from its use. If you copper or lead
faster than 20 shots, you will need a second kit or stronger measures. If
bore finish (friction) is what was negatively affecting your accuracy,
accuracy will improve from this system.
If you still have trouble understanding
this process, think about sanding wood. Using any grade of paper, if you
push harder, more wood is removed. Think of sanding a sharp edge and how
the paper cuts quickly at first and slows as you widen the sanded surface.
And lastly, new paper cuts better than old or loaded paper. These are the
same principles with metal and fire lapping. If your bore surface is
smooth already, then cutting will be slower and less metal removed than if
you have pretty bad tool marks. But the rate of cutting action will
eventually slow as a smooth surface is reached. The slug will cut less
once it loads up. The earliest threat to a rifle is throat wear because it
is vulnerable to removing too much metal before your goal is reached. So I
will address some tricks for minimizing or preventing (not eliminating)
The best method for eliminating throat
wear is not to fire more lap bullets than necessary. Just think how to
make each slug fired more effective at what you “need” done if this is
possible. If I wanted to just clean up minor dimensions of a rifle barrel
without removing much metal at all using lead, I would do the following.
First, I use one bullet hardness standard for every procedure I attempt
regardless of gun model or steel type until I gain enough knowledge to
change. This is so I can gain knowledge to use towards my next lapping
project. ACWW works great. WDWW cuts faster. And the hard bullet base is
stronger to resist obturation in the throat. I lap rifles with one size
grit only. That is 320. Coarser can leave deep scratches if you don’t need
to remove much or cut too fast. And finer grits are a waste of time since
I can use the Tubb’s System to polish without worrying about throat wear.
Next I would buy a Lee push through
sizer .001 smaller than my current bore diameter. Remember that a bullet’s
diameter will increase a few thousandths as you roll it in the lapping
compound. The diameter increases more as coarser grits are used. The Lee
sizer will take the major wear out of my throat now that my throat is not
performing the sizing function. Next, I would lightly coat the bore with
oil so that my “stone” doesn’t load up before it gets to the end of the
bore. And then I would clean after each shot and reapply more oil to
continue the same process. Then slug, slug, slug as I go. This is
obviously to monitor throat wear. I will need to slug the throat and then
push one all the way through using a light coat of oil to tell me when I
am close enough. Always stop before perfection is achieved. This is
because dimensional changes will continue until a truly smooth surface is
reached either by using jacketed or cast later. Most dimensions will
open up anther .0005 from this burnishing just shooting the gun normally.
Since you opened the pores of the
steel, about 20 jacketed will be required to burnish it again using the
shoot clean, shoot clean method for at least five shots. If you have an
aversion to jacketed bullets in your bore, then expect 200 rounds of high
antimony lead or maybe 500 ACWW before you can run higher pressures with
soft lead (less than 14 BHN) again. Hard lead may actually perform better
with this surface, but it only lasts until it is smoothed back to normal
You will actually learn a lot from
lapping the LEE sizer before you begin. You will roll your first bullets,
size them, and throw them away until the sizer gets lapped out enough to
get close to the diameter of your bore. You will discard the first bullets
until you reach your bore diameter. You will see that the first five lap
bullets open the die diameter about .0005. During this time, manual
pressure from the press is easy to push them through. Then watch as it
takes many more attempts to get up to .001. That is because the inside of
the die is tapered and you are only removing a few tool marks at first.
Then as those are removed and the metal doing the sizing is increased in
length, the diameter gets slower and more difficult to cut. And the manual
pressure you need to size the bullets will become more difficult. This is
what your throat and rifle experience as you lap. And also why the oil
When you get the diameter of the die so
that it can size a bullet to the same size as your throat, minimal
enlargement or lengthening of the throat will take place as long as you
don’t use too much pressure from your load.
This also minimizes the chances for a stuck lapping bullet and allows even
less load pressure to control obturation in the throat. This lapping of
the Lee sizing die teaches you the process. Using the correct size lap
bullets, along with low firing pressures, and cleaning between shots and
applying light oil again are the biggest steps you can take to prevent
enlarging the throat and achieving an excellent result with the fewest
If I had a constriction in my barrel
under my sight, I might try and hand lap it first if it was more than
.002. Then using the steps described above, I would add a coating of Lee
Liquid Alox, that came with the sizing die, over a gritted up cast bullet.
This slows the cutting effect until the bullet reaches the constriction
where sizing pressure increases the cut at that point. Handguns are very
similar to the just described procedure for removing a constriction in
rifles above except that you don’t have to worry about elongating the
throat. Just about putting a taper in your throats. This also helps keep
the abrasive from breaking free and cutting the end of the barrel or the
cylinder face and enlarging your barrel / cylinder gap. Or getting into
the mechanical areas that we don’t want it
Handguns receive a two step lap
process. If I am interested in removing a constriction in the forcing cone
without enlarging my throats I would now go to 220 grit for my abrasive. I
would seat my bullets out as far as I can get away with and hold the
bullet diameter at my current “bore diameter” until the constriction is
removed. I would start with WDWW. I would clean and oil after every
cylinder full. And slug after every 2 cylinders. How many shots this will
be is anyone’s guess. I have seen as little as 24 to over 60.
Once I was within .001 of removing the
constriction, I would change to ACWW and 320 grit. And I would use the
Liquid Alox. I would now increase bullet diameter to match my throats.
What my intention is now is to clean up the throats from the 220 grit
damage. The forcing cone will clear up because for each one pass of a lap
bullet on a cylinder throat, the barrel sees 6 shots. I would figure on 18
shots to clean up a stainless and maybe 36 for a chrome molly barrel. Then
I would go to jacketed for about 100 rounds to complete the job and
burnish the steel. Winchester makes some sort of hollow base bullets that
are cheap and the base swells out to deform into a complete burnishing
system. This is especially good for forcing cones to smooth areas smaller
diameter bullets might not reach for many rounds. Then if you go to a
large diameter cast and still see a little light flake leading in the
cone, you may assume the lap was unsuccessful. Give the gun a couple of
hundred rounds before you form any opinions.
You do not have to remove enough to
create a taper. If you do create a taper, you move the forcing cone
forward. This means that short light cast bullets may break the seal on
the throat of the cylinder before it seals the bore. That means gas
cutting and not being able to shoot light bullets. If you are strictly a
heavy bullet guy, then by all means go for it. When you shoot the taper in
you are creating a Taylor Throat that some people swear by for revolver
accuracy. When you are sure that you are completely finished lapping to
your satisfaction, the gun should be disassembled and cleaned thoroughly
before moving on to burnishing the bore. This is another reason to avoid
the really fine grits. They tend to work their way into mechanical areas
during the lap process when dealing with a barrel / cylinder gap.
The only thing I have not covered is
load data. And this is because this is the wildcard that makes or breaks
the entire process. I use a computer program called Quickload that allows
me to see and adjust pressure based on my first shot. And I do
chronograph. Or at least have a background out there that I can ensure
that a bullet exited every time. The goal is consistent pressure; which
means a fast for caliber powder and a magnum primer to ignite it. We are
not interested in groups here, but we don’t want a pop fizz to stick one.
If you are doing a rifle case, you may need a filler. Try and pick a load
that develops 600-800 fps if possible. Remember the lesson from the sizing
die. The first ones cut easy and get more difficult to push through as the
bore cleans up. If you are going to stick one, it will likely be after you
think you got the hang of this. Use the oil please.
I hope that this has given you enough
insight into my thought process and enough knowledge to decide if you
should try fire lapping.
My own opinions, John Cox
After reading quite a bit about fire
lapping, I was sitting on the fence. On the one hand, I don’t like the
idea of wearing out a rifle earlier than I need to. On the other hand, if
it can help improve the accuracy of a rifle – so much the better.
Don’t goop up a patch with Valve
Grinding compound and swab it up and down the barrel and think you are
lapping. This sort of thing is a quick way to turn a decent barrel into a
bad barrel. Reasons:
You will bell out the barrel wherever
you change directions – so if you are “Working” a tight spot – you may
relieve the tight spot, but will also create a loose spot directly before
and after the tight spot.
Patches absolutely do not maintain
geometry – you will lap the barrel egg-shaped.
You will definitely wear down the
rifling faster than the bore groove – as the patch presses harder into the
rifling than into the groove.
Reasons to fire lap:
Constriction or tight spot in the
barrel – These cause fouling and can hurt accuracy
To reduce barrel leading by smoothing
out tool marks in the rifling, especially in factory barrels.
To create a slightly choke-bored
rifle – where the bore is slightly smaller at the muzzle end.
Reasons NOT to
All Lapping operations are usually
good for surface finishes, but can be bad for geometry – In other words,
unless you are a PRO, lapping a round hole can result in an egg-shaped
Lapping does enlarge the rifle
throat. The leade is the first thing the lapping bullets hit – so it
wears the most.
Your barrel inside diameter is
It is usually unnecessary for a
hand-lapped match barrel – unless it is a 10,000 round E-bay special.
Reasons to Fire
Lap instead of hand lapping
Hand lapping an installed rifle barrel
results in belling of the muzzle and the throat – or anywhere you change
directions with the lap. If you short-stroke a lead lap in your rifle’s
throat end of the barrel, you will bell out the barrel ~4-6” from the
chamber end, and also at the throat.
Hand lapping can damage the rifle’s
chamber if you pull the lap out and hit the chamber or if the rod rubs
against the side of the chamber.
Hand lapping can ruin the rifling if
the lapping rod rubs against the rifling
You will lap your bore out of round if
don’t get good even coverage of the lapping compound.
You will lap the muzzle larger than the
throat – if you always cast and charge the lap from the muzzle end.
Here is the method I have settled on for now:
Oversized cast lead slugs. Unhardened
Lapping compound – NO coarser than
300 grit. Silicon carbide seems to be the general consensus now – and
there are many sources including quite a few commercial kits, Clover
2-rolling plates. Plate glass, flat
steel plates, etc. Wood is a bad choice as it soaks up the abrasive
Once fired (but not resized) cases
that fit your gun. Range pickups that will chamber work great here.
These will be throwaways – so don’t use your new $5.00 per shell Lapua
or custom Bertram brass unless you have absolutely no other choice.
7/8-14 bolt – to screw into your
press to seat the bullets into the case (Lapping compound is hard to get
back out of a sizing and seating dies)
Small punch or universal de-capping
die to knock out primers.
Stout cleaning rod or piece of
all-thread wrapped with electrical tape and a nice heavy hammer or block
of wood -- as an Emergency Bullet Un-Sticker
Chamber cleaning brush and cotton
patches – to swab out the chamber between shots.
Dab some lapping compound on the slug
and roll between plates until the bands are completely impregnated with
Fill the grease grooves with compound
Load with Red Dot, Unique, or some
other extra-fast pistol powder to the bare minimum velocity required to
pop the bullet out the end of the barrel (like 2-3 grains of powder in a
30-30, Velocity around 400-600 fps or so. The bullets hit 12-20 feet low
at 100 yards…) Don’t use rifle powder – as “Secondary Explosion Effect”
may be a hazard.
Use your 7/8-14 bolt into your
reloading press to push the slugs into the cases.
Yes, it is a greasy, gritty mess. Don’t
handle your guns or equipment without cleaning up your hands. Wipe down
the cases before you shoot them unless you want scratch marks all over
Save that brass from each round for the
next round of your fire lapping with that gun – don’t resize them after
you shoot fire lapping bullets – they didn’t have enough pressure to
expand them at all.
At the Range.
Bring your taped up all-thread rod and
hammer -- You will stick a bullet.
Bring your chamber brush and plenty of
soft cotton patches – your chamber really does not like lapping compound.
You have to swab the grit out the chamber between shots.
Load one cartridge into the chamber at
a time, not from the magazine, and fire.
Listen for the “Thwap” of the bullet
hitting dirt at each shot, check down the barrel with an open chamber
between shots - just in case.
Shoot 5-10 bullets, then clean it out
and check for progress.
When you stick one (Oops, forgot the
powder) – Unload the gun and Stick the cleaning rod down the muzzle end,
and give it a whack to pop the bullet back out.
Fire lapping smooths out the barrel, so
you get lower velocities (and pressure) than you did with the same load
previously – unless you had a giant constriction at the throat. You will
need to work up new loads over the Chrono to duplicate your old loads
It takes 10-30 rounds for the barrel to
settle down after lapping. If you have a chrono, you can watch the
velocity go lower and lower with each shot, until the bullets burnish the
lapping scratches out.
How do I know
if I am making progress
Marshall Stanton (Beartooth) and Veral
Smith (LBT) both state that you keep going until the constriction is
relieved (check with a tight patch on a cleaning rod or with a soft lead
sinker slug) or if you don’t have a constriction, until about 1/3 of the
little tooling marks on the rifling inside the muzzle are gone.
Marlin 30-30 with huge constriction at
the Throat (0.304” at the throat, 0.309” at the muzzle.) The Marlin took
about 100 fire lapping shots to open up the constriction. The rifle shoots
much better than it did, but needs 0.310” dia oversized bullets now. (It
averaged 8”-12”at 100 yards, now it runs ~1”-3”)
Remington Heavy Barrel 308 – Rifle had
a large tool mark about half way down the barrel. The barrel fouled like
crazy. The first group averaged 1”, got worse each group afterwards. 20
lapping rounds later, it averages under 3/4” 5-shot groups, and goes >50
rounds before 5-shot groups open up to 1”
Yugo Surplus M48 8mm Mauser. Tried out
the Tubbs Fire Lapping Kit on this one. This rifle probably was not a good
candidate for lapping with jacketed bullets, as the barrel was oversized
to start with (0.324” vs. 0.323” spec.) The barrel smoothed out
considerably, but was still inaccurate due to the oversized bore and
Beartooth Bullets Technical Guide, J.
Marshall Stanton, Beartooth Bullets, Dover ID, 1993
Jacketed Performance with Cast Bullets, Veral
Smith, LBT, Moyie Springs, ID, 1984
LBT Bore Lapping Instructions,
Veral Smith, LBT, Moyie Springs, ID, 1984