The Los Angeles Handgun, Rifle, Air Pistol, Hunter/Field Pistol Silhouette Club

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A collection of comments and articles on the many aspects of bullet casting by various cast bullet shooters
Cast Bullets For Beginner And Expert
SECOND EDITION, 2007 - Joe Brennan

Fire Lapping Barrels

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 period.

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 Barrels

Ken Mollohan

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 ruinous.

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:

Equipment:

  • Cleaning rod

  • Bore mop

  • Patches

  • Cleaning solvent

  • JB compound

  • Especially loaded ammo (See special notes below)

Procedure:

Take everything to the range, and proceed as follows:

  • 1. Remove the bolt from the rifle.

  • 2. Coat the bore mop lightly with JB compound.

  • 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 progress/improvement.

  • 8. Repeat as necessary.

Special notes:

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 observed.

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 risk.

Ken Mollohan

"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 there.

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 none.

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 wrote it." Charles Graff

(Lapping the 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

John Robinson

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 not.

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 point.

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) throat damage.

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 again.

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 helps.

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 bullets possible.

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 in.

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. John Robinson

Fire lapping barrels

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.

One basic caution:

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 fire lap:

  • 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 hole.

  • 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 already oversized.

  • 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:

Supplies:

  • Oversized cast lead slugs. Unhardened lead.

  • 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 compound, etc.

  • 2-rolling plates.  Plate glass, flat steel plates, etc. Wood is a bad choice as it soaks up the abrasive compound.

  • 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.

Instructions:

Dab some lapping compound on the slug and roll between plates until the bands are completely impregnated with grit.

Fill the grease grooves with compound as well.

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 your chamber.

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.

Other observations:

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 velocity.

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.

My experience

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 off-center throat.

Further reading:

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

 

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Warning: All technical data mentioned, especially handloading and bullet casting, reflect the limited experience of individuals using specific tools, products, equipment and components under specific conditions and circumstances not necessarily reported in the article or on this web site and over which The Los Angeles Silhouette Club (LASC), this web site or the author has no control. The above has no control over the condition of your firearms or your methods, components, tools, techniques or circumstances and disclaims all and any responsibility for any person using any data mentioned.

Always consult recognized reloading manuals.

 

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