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I don't believe the taper of a throat is much of an issue. When Harold Vaughn did his accuracy work on a .270 Sporter rifle, which he finally got to shoot .25 moa groups, he used a chamber reamer he made himself with a very shallow 3/4° taper. Note, too, that if you shoot many full-house loads with H110/296, the throat of a magnum revolver erodes to a pretty smooth state anyway. I think you simply accelerated the process.

If you look at jacketed bullets recovered from a berm, in which they stopped slowly enough not to deform appreciably, you often see little tabs, like tails at the ends of the impressions made by the rifling lands. That's gilding metal smeared by friction dragging it back. Bullets are swaged into a bore under pressure, same as they would be in any other shaping die. Absent saw teeth on the rifling, there is no way for it to cut the bullet metal. It just squeezes it to shape.

The only concerning thing you mentioned was asymmetry of the lands at the throat of the barrel. That's not good as it could lead the bullet to tip slightly into the bore. I don't know what caused it for sure, but suspect that if you cocked your empty revolver and used a light source and white paper behind the chamber, you would see the cylinder alignment was slightly off. A gunsmith can correct this, getting the slop out of the cylinder bolt (aka cylinder stop; the tab that goes up into the notches in the cylinder from the bottom of the frame) and correcting its location to line the chambers up correctly. Unfortunately, this can sometimes mean also installing a new pawl, as the corrected cylinder lock-up may be further around the clock than the existing hand will push it.

In your case, if it's not the barrel you removed, you may be able to re-ream the throat. I have used a toolpost grinder on my lathe to correct the worn throat of a revolver barrel before, but the barrel had to be removed from the frame to do this and the throat angle has to be made a fraction shallower than original to avoid opening up the back end of the forcing cone. I don't find that steeper angle hurts anything, though.
 

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Hey Uncle Nick -
What you say is very interesting.

I would be getting in deep for my skill level to attempt a barrel removal and rebore. The pawl is probably OK because the gunsmith (who is really well known and respected) did pawl work and faced the cylinder square so the gap is the identical all around. If necessary, I would send it back to him, but the shipping for firearms is a price I hate to pay.

Because I can't see straight up the barrel from the forcing cone end, I was thinking of plugging the front 6-1/2 inches of the barrel and casting a slug of the forcing cone and beginning of the lands. When cured, I would knock out the casting and be able to see what the forcing cone and beginning lands look like.
I was thinking of doing it with some filled epoxy (I am a plastics pro and have some never-fail polymer releases so the epoxy would not stick to the barrel) unless you can suggest another casting material that would be easy to use, hard and stable. 2 part mold making silicone would be ideal, but I am out of that.
 

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I would look with a borescope first. The shadows and light and awkward angle can fool your eye into thinking an error is there that isn't, and vice versa. Also, if you put the grip frame in a vice, muzzle up, and hold a dental mirror under the forcing cone, you might be able to shine a flashlight from your vantage point to bounce off the mirror and illuminate the throat and forcing cone area while you look at it in the mirror.

The classic material for a casting would be Cerrosafe, which is used to make chamber casts. Molten sulfur would be the old school way. Cerrosafe is a low melting point Bismuth alloy that is known to shrink slightly during the first half hour after casting, letting you knock it loose, then growing over the following half an hour to match the actual size of the the chamber, then afterwards it gradually gets a little bigger. So it's used with the object of measuring it when that one hour matching dimension post-casting point in time arrives. But in your case it sounds like all you want is a relative picture of the throat condition to check for symmetry, so casting from any 2-part resin, be it an epoxy or a polyurethane like Flexane 90 or from a two-part silicone would tell you that much.

I'd be interested to hear what your never-fail release agents are, if they are generally available.
 

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Release agents

Nick -
You gave me some excellent firearm detail; I hope this answers your release question. This could be handy info for any inventive person (which includes lots of people on this forum) who want to make custom things out of fiberglass. Aside - anyone who wants to experiment should use the WEST System epoxies, with their easy metering small cans of product. I alway keep some in my home workshop (epoxy has a nearly unlimited shelf life) and some WEST 404 filler powder that makes a nearly shatter resistant compound (it is **** to sand a fully cured 404 patch.) They have lots of helpful info at their website: Epoxy by the Leading Epoxy Manufacturer | WEST SYSTEM Epoxy or use System Three - System Three Resins, Inc. products.
Now about release agents: I doubt these release agents are sold retail in small quantities, but I have never looked. Standard packaging is quart or gallon cans. Almost all shops doing molding use this type of product, and maybe one of those would sell you some. A new polyethelene squeese-type ketchup bottle is a good container to transfer the release into. If you are making something only a couple of square feet in surface area, a few ounces of release liquid is sufficient. A seal cap is necessary for storage or the release will go bad. They are micro thin polymers in liquid, mostly water clear, that are applied as a wet layer by wiping or spraying on a clean stripped surface, then immediately wiped off with a clean absorbent cloth so each layer is applied evenly. Wipe on, wipe off, about as quickly as the time it takes to read this sentence, and it dries nearly instantly. Then wait about 30 minutes between coats. After 2 or 3 coats, do a tack test with masking tape and if there is no problem with the agent such as contamination or expiration, the tape will not stick. Then proceed with product sprayup or casting. Multiple releases are expected. Do a tape test after every part is pulled and add a layer of release if the tape has a little adhesion.
These are wonderful compared to the old paste waxes we used because there is no build-up. With polyester resins (that new boat smell) the paste waxes would build up to a hard crust, leave a rough finish on the part, and take a lot of nasty work to refresh the mold.
On a strip clean barrel, I will apply it with a cotton cleaning patch and follow immediately with a dry cotton patch. I will be very cautious about making a casting at my barrel throat, because the high adhesive epoxy has the potential to make my gun Homeland Secure :eek:

About 40 years ago, these were introduced. There are lots of manufacturers now. In recent years I have been using Zyvax because they invented a line of water-based releases. The originals and most others are still using volatiles that require a respirator, melt some types of gloves, can enter the blood stream through skin, and evaporate rapidly, so only small areas can be coated before the requisite wiping. Others now offer water-base releases.
For more detail, Zyvax has a good website: Zyvax Mold Release Agents, Mold Sealers, Mold Specialty Products and Mold Cleaners
A few others: Frecoat is one of the originators http://www.henkel.com/44-nc-21466.htm and there is AXEL Mold Releases and Process Aid Additives Home Page | Axel Plastics Research Laboratories, Inc. and Mold Release Agents, Casting Lubricants & Other Manufacturing Aids | Chem-Trend
 

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The Hog Whisperer (Administrator)
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Wow. Dave, that's really great info.
 

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Yes! Thanks.
 

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Handlapping is tricky, its a **** good way to damage the throat of a rifle for one thing, but with care it can be done..fire lapping is the best method, but in truth is mostly BS that just makes folks feel better..I used to break in barrels with all the accepted methods, but unless your a target shooter its an exercise in futility..most barrels either shoot or they won't in the real world..

Lapping is nothing more than wear on the barrel, so you can get the same results with just shooting the gun...I have a friend that bought a 1/2 inch shooter and he spent a week lapping it and now he has a 1/2 inch shooter with a really smooth bore...

I'm primarily a hunter, my guns shoot fine and if they didn't I'd get rid of them..I see no use in lapping and it boils down to the difference in boys and men is the cost of mens toys IMO...
 

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Big 5,

Can't agree. There's a past issue of Precision Shooting wherein Merrill Martin (IIRC) firelaps a wheel gun, showing the targets he printed with the fire lapping bullets. The first six made a six inch group (50 ft, I think), the next six not much smaller, and then the third six go into about an inch. Also, NECO ran firelapping loads through 27 U of SF rifle team smallbore barrels and got an average accuracy increase of 15% from firelapping, despite these being match rifle barrels to begin with.

Firelapping usually improves lead bullet accuracy, but may not affect jacketed bullet accuracy. I've had that experience on two rifles. But they are a heck of a lot easier to clean. My first Garand's military barrel used to foul so badly that after 35 to 40 shots it began dropping points. Then it would take me hours to get it clean, with patch after patch of Sweet's 7.62 going through it and turning dark blue. That's what first drove me to moly bullets, which didn't foul that barrel enough to cause that problem. But when I later firelapped it, that problem was gone regardless of what bullet I used, moly or no moly. Based on the number of patches of Iosso Bore Cleaner (mild abrasive) and the number of strokes required to clean it between 5-shot sets of firelapping loads, ease of cleaning improved by about a factor of 6. Rate of fouling was likely reduced by a similar amount.

The other thing that happened with the Garand is that it had a bore constriction of about half a thousandth of an inch where the barrel contour thickens below the lower band and all the way back to the throat. Firelapping cleared that out. This was a well-used military barrel with probably 3,000 rounds through it before I started, and no amount of regular shooting had done anything to reduce that constriction. The constriction didn't seem to bother jacketed bullets much, as, after bedding and before firelapping, the rifle put its first 10 rounds into 0.7" at 100 yards from prone, which is pretty good for one of these old battle horses. But cast lead bullets? Forget about it. With that constriction they grouped in shotgun patterns. Only after firelapping did that stop.

The bottom line is that firelapping doesn't reduce the metal in the same pattern as bullet wear does. I think that's partly because the much higher temperature and pressure of normal loads causes heat stress cracking that promotes throat erosion in a rifle long before bullets can wear the bore portion. Indeed, rifle barrels are set back and cut and recrowned all the time, and often more than once in their lives, but the middle section of the rifling remains in good shape. In another thread one of this board's members describes a test done by the Garand Collector's Association in which 60,000 strokes of a steel cleaning rod, carefully biased around the clock, did not deteriorate accuracy or increase measured muzzle wear. This leads one to conclude most cleaning rod muzzle wear is caused by dirt and grit on the rod, rather like an abrasive lap. So, it's pretty hard to imagine a softer bullet jacket doing much of anything within a reasonable number of rounds.

The other factor is that the pressure in firelapping isn't strong enough to bump a jacketed bullet up much, so it tends reduce a constriction, then be too loose to abrade aggressively beyond it. This is why, as Veral Smith points out in his book, harder firelapping bullets make straighter bores, while less hard ones taper a bore down from breech to muzzle, tending to bump up in the bore at the throat but lose contact force as pressure drops going down the bore. Very soft bullets tend to polish a bore surface evenly, as they bump up wherever they are in the bore, and so do not relieve constrictions.

In the case of my Garand, I used pulled M2 ball jacketed bullets and NECO's laboratory grade abrasives to opened the constriction up the required half a thousandth of an inch plus a ten thousandth more, but the muzzle opened by only a ten thousandth (slug measurements), and I landed with a straight bore.
 

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In agreement with Unclenick -

The several rifles I've firelapped with the NECO lapping kit all improved in accuracy and are much easier to clean than before. It's not magic, but in most cases it helps to some extent.
 

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I've got a question on, for better words, "maintenance loads" which is a form of fire lapping, just with a very fine grit and what ya'lls take on those. Seems like since David Tubbs started selling his is coated bullets for what he call maintenance loads, and sold the idea to the public, a few other companies are coming up the different solutions to do that. One in particular is KG-2. I've experimented with that in a couple older barrels and don't know that I've seen any difference, but again, I've only used it once each in two barrels and have yet tried it in a fairly new barrel. If you read their claims, the military snipers use it and it increase barrel life and improves accuracy.

Not saying a company would over state just what a product will do, just to sell it, but I have a tendency to take a lot of sales propaganda with a grain of salt.
 

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AFAIK, the Tubb's maintenance kit is meant to maintain the throat and bore polishing work done using Tubb's Final Finish kit first. It's like a touch-up fire polishing kit for the Final Finish system.

Tubb's Final Finish uses long jacketed bullets with relatively fine graded abrasives, and fires them at normal starting loads, which is to say, way above the usual firelapping loads. This has the effect of keeping the bullet upset out against the bore so the resurfacing is even and is not cutting out constrictions and the like. But it will remove alligator pattern heat stress cracked surface from your gun's throat. You could do this with any firelapping kit, substituting finer abrasives for polishing.

If you go to the LASC site and search on 'fire lapping' (they make it two words instead of one, and I've seen it both ways for awhile now), here, you'll find one fellow prepares revolvers for lead just by polishing rather than actually ironing out constrictions. Apparently he just uses soft enough allows to bump back up after passing through a constriction, but having the surface smooth allows that to happen without depositing lead. If you want to shoot really hard bullets, you still want to rid yourself of the constrictions. Anyway, he just puts JB Bore Compound in his barrels and fires a light load into them and repeats until the barrel is smooth.

I think you'd get the same effect faster by rolling soft lead bullets into 400 grit compound until you saw it smoothing the muzzle, then going to 800 and then 1200 grit, as the NECO kit does. You could even finish off with Flitz or JB in your bullet's lube grooves. The NECO kit uses lab grade abrasives with smaller particle distributions than the standard Clover compounds have. This cuts about twice as fast, according to telescope makers. So if you want to try it, those more expensive abrasives from NECO might save you some time.
 

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Is it something you would recommend doing? KG products recommends doing it after every several hundred rounds. Since I'm kinda sensitive about putting any kind of apprassive material in any precision, hand lapped barrel, my question was if this would be a recommended process or not. You seem to be about one of the most knowledgeable people I've come across about a lot of this stuff, and would trust you input way more than some manufactors claim to fame.

I've fire lapped barrels since the late 60's and had good intial success, but it seems the accuracy life was short lived. I fire lapped my first 6mm 788 I bought when they first came out, it was ungodly accurate, but within 600 rounds it lost everything gained and then some. I've also done several other factory barrels over time doing some of my accuracy tricks, but I've always used special, lapping compounds in 600, 800, 1,000, 1,200 and then finish up with some special polishing compounds. I have hand lapped a number of barrels also but only before being chambered and cut to length, so I could get rid of the oversize areas reversing the lap caused. The thing is, for the past number of years, as I've been replacing barrels, I've been getting high quality, hand lapped and polished, air guaged blanks and those, I'm very sensive about what goes in them.
 

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Your comment about the short-lived accuracy of the firelapped barrels is interesting and not something I've heard before. I didn't hear about fire-lapping until I got Veral Smith's book sometime in the late 80's, so I don't know what methods or materials you were using before then. Tubbs claims he can take a barrel that is starting to get symptoms of being shot-out and double it's life by renewing the throat and resurfacing the bore with his kits.

It would have been interesting to see if a second firelapping would have revived your 788 or not? My expectation would be that once you achieve a new geometry, steel should take awhile to change. I have noticed that firelapping can round the lip of a crown considerably by the particle blasting outward over its edges, and so I have recrowned after firelapping. I don't know if you tried that.

In the 60's and 70's modern bore cleaners weren't around (I was still using Hoppe's #9 then), so, after crowning, the first thing I would have suspected for your 788 was a build-up of some kind that remained invisible to the naked eye and didn't easily show on a patch. A bore scope would have been an interesting tool to have been able to apply to those barrels. The other possibility that occurs to me is that it's possible to overdo it and iron out the throat too much. That might be caused by the choice of abrasives. The particle size distribution is quite large in the standard grades; over 3:1 in diameter. This has two effects. One is the possibility of coarse particles getting wedged in a way that inflicts deep scratches. Another is the extra fine particles tending to pack around the larger ones and slow cutting action so that you need to shoot more rounds than you otherwise would, giving the first problem more opportunities to occur.

Abrasive choice affects hand lapping, too. Silicone carbide cuts fast, but the particles are often shards that are longer than they are thick or wide. These get laid over pointing rearward as you push the lap down the bore, then present an extra sharp set of teeth when you first reverse the lap and until they are laid back the other way. If you use aluminum oxide, which typically has a less irregular and less sharp particles, it will cut more slowly but have less tendency to enlarge at the direction reversal site.

I have no experience with the KG-2 product. I've used JB Bore Compound and Iosso Bore Cleaner (another abrasive cleaner) with good cleaning results, but have not attempted to evaluate the theory that leaving copper and carbon in the gun's surface imperfections will reduce fouling shot requirements or improve first shot POI. I do remember Merrill Martin's article on Carbon Tunnel Syndrome, suggesting a thin carbon layer needed to be established for best shooting. But that wasn't just in the surface imperfections. That was down the whole bore surface.

Varmint Al wrote that he has abandoned conventional break-in's in favor of 50 strokes of polishing with Flitz. He says that if copper fouling still builds too fast he does 50 strokes with JB Bore compound (I forget if he follows that with more Flitz; I would). This is presumably be on hand-lapped custom barrels.

My current system for lapped barrels involves about 40 strokes of Iosso Bore Cleaner (20 per patch; my patches are actually pairs of patches wrapped around an undersized Nylon bore brush) with each stroke going a few inches down the bore, then back, gradually progressing down the bore in this jerky fashion. Starting at the breech is to ensure the greatest abrasive action is at that end, so that if there is any microscopic tapering, it is from wide to narrow at the muzzle. This also evens out the abrading action down the tube. If I had a standard factory bore, i would do this after any firelapping I might find necessary to do.

The patches I run through that way come out black, so they've picked up some amount of metal. Iosso Bore Cleaner has not got any petroleum products or wax in it that I can smell, so it won't leave that behind in the bore waiting to be carbonized by heat. It appears to polish pretty well. I then run ten rounds of shoot-one then clean-and-cool. This is just in case there is merit to Howa's distributor's claim the barrel takes a set in the cold barrel position over the first shots. I wish there was an economical way to prove that one way or another, but unless someone wants to fund a bunch of test barrels and a control group of barrels, I'm not going to be the one to prove it one way or the other. I just figure 10 shots isn't enough trouble not to go ahead and do it, just in case it's true.

The Howa guys seem to think it's a big deal to leave no petroleum products in the bore between break-in shots, where they form carbon when exposed to propellant head. They recommend cleaning with Windex to avoid carbon. I use Boretech Eliminator for the cleaning, then Windex to remove the Eliminator traces. Bore scrubber or carb cleaner would probably remove traces, too. Eliminator just cleans carbon and copper a lot faster.

After that, the barrel gets cryo-treated. I've read a couple of studies on cryo-treating showing it really does improve wear resistance. Improved rifle barrel temperature stability is long-standing claim in the cryo-business, but I am unaware of anything but anecdotal reports of this. The scientific community has not taken notice of shooter's problems.

One of the recent papers on the subject¹ includes both shallow and deep cryo-treatment of tool steel. And while the usual deep treatment (liquid nitrogen; around -330°F for 24 hours) had the effect of converting virtually all retained austenite (19% was retained after regular heat treatment) to martensite, the tidbit that caught my eye in that study was that shallow cryo-treating, which was just going to dry ice temperature for 8 hours, got almost 75% of it converted. So, on the theory that some conversion is better than none, that's what I am going to try on a couple of barrels (I can get dry ice at a local ice cream factory). Given all the liquid nitrogen used in molecular gastronomy these days, that's probably more widely available than it used to be, too, but I haven't gone shopping for it.


¹ D. Candane, N. Alagumurthi, K. Palaniradja. Effect of Cryogenic Treatment on Microstructure and Wear Characteristics of AISI M35 HSS,
International Journal of Materials Science and Applications.
Vol. 2, No. 2, 2013, pp. 56-65. doi: 10.11648/j.ijmsa.20130202.14
 

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There are break-in procedures, and cleaning with JB or Iosso Bore Cleaner will get them to progress a little better than just patches and solvent, but they don't truly lap the bore.

For true lapping you have basically two alternatives: hand lapping and firelapping. The first normally uses a lapping slug on the end of a cleaning rod that is cast into the muzzle of the bore by plugging the bore back an inch or two with patches or paper and pouring molten lead into it. Grooves similar to lead bullet lube grooves are cut into the cast slug with a knife or a gouge to hold abrasive compound. The lap is loaded (the grooves filled) with abrasive and run back and forth in the bore by hand. It's s common to use something like 320 grit silicone carbide lapping compound (Clover compound, for example). The slug is usually pure lead so that when it encounters a constriction it is narrowed and does not spring back out after passing through it. In this way all abrading on subsequent strokes is only in the tight spots. When you feel it stop cutting tight spots, you can bump the lap back up with a brass rod and hammer, and go at it some more. You keep repeating until the bore has no more tight spots and the lap feels smooth down the length of the bore.

The other method is firelapping. This involves shooting abrasive embedded bullets through the bore with very light loads that get low airgun velocities (300-500 fps). The lapping bullets are usually cast bullets in the hardness range of 10 to 12 BHN. This number range is a compromise. It doesn't limit itself to cutting constrictions as completely as pure lead laps on a rod, but it is malleable enough that it doesn't lap the wide places nearly as hard as the narrow ones. The reason it isn't pure lead is that where a pure lead hand lap can be pushed through a constriction by rod without bumping up, when you have even firelapping load pressures on the base of a pure lead bullet it will bump up to rub the wide spots as well as the narrow ones. At the other extreme, an alloy bullet of higher BHN is surprisingly elastic and will go tightly into the bore and stay tight all the way down its length, thorough narrow places and wide ones. That tends to remove material evenly everywhere. You don't want that because, while it widens tight spots, it widens wide places equally, so you don't level off major irregularities; you just smooth those shorter than the length of the slug. When you are done firelapping, irregularities are gone and it leaves the bore very slightly tapered down toward the muzzle. Maybe a half thousandth or so. This is considered desirable for accuracy, especially when the bore is to shoot lead bullets.

Either lapping method will reduce metal fouling, making the bore easier to clean. Firelapping has the advantage that in addition to introducing the slight taper, it also cleans the throat up. Hand lapping does not normally clean the tool marks off the throat because the rifling is cast into the slug when you pour the lap.

The board sponsor, Beartooth Bullets, sells a firelapping kit, here.
One comment, if it's a Kreiger, they have their own suggestions and pretty much don't really need lapping. It's why I use their barrels aside from the quality and accuracy.
 

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It's always best if you can get a bore that was factory lapped. They generally do that before the blank is trimmed and chambered, so that if the lapping process should funnel the ends of the hole slightly by reversing the lap, that's the inch or so of barrel cut off the blank after the contouring is done.
 

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Lapping a bore is wear, plain and simple, I would rather shoot about 200 rounds through one of my rifles than lap a bore. Most rifles pick up their finest accuracy at about 200 to 300 rounds, its just another way of lapping IMO..If you purchase an accurate rifle then lap it you gain very little at best in accuracy, and pushing stuff down the barrel can also be risky as more bores have been ruined by cleaning rods than shooting. To each his own.

I use mostly Lothar Walthar barrels and I defy anyone to improve LW barrels by lapping, they come finished and they have a patented lapping process. Lapping compound would actually make them rough.
 

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I don't know anyone who has firelapped a hand-lapped barrel. At best you would be duplicating effort with less controlled conditions. It's the rough, funky factory barrels that often benefit.

Well, now I have to take a part of that back. I do know a cast bullet shooter who firelapped a Hart barrel that was cut down and set back and rechambered for a second life. He was specifically trying to establish a slight tapering down from breech to muzzle for cast bullets, which can be done with the right lapping bullet hardness. Of course, his cast bullets are sized to the bore, so bullets being undersized is not a problem there.
 

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Rest my case Nick, its all wear/polish on the barrel..

.Never said it didn't work, it does, basically said it was a waste of time for me..or perhaps a short cut to more accurate shooting and less barrel life....

From a hunters standpoint it not a particularly good practice and a waste of time or fun an games for some..Just my opine but I'm not a bench rest or target shooter...

If I had a inaccurate barrel I might lap it, might even fire lap it to save time, but my experience with barrels is they either shoot or don't shoot and if they don't I install a new one.
 

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But sometimes barrels shoot well, but foul badly. That's another thing lapping helps with. Not everything comes with a hand lapped full custom barrel and the rest of us sometimes need to lap barrels.
 

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Rest my case Nick, its all wear/polish on the barrel..
But it's different from normal bullet wear. If you've got a borescope, you'll have noticed normal firing wear does very little much beyond the throat. Also, the throat wear takes the form of thermal stress cracking which causes the alligator skin pattern in the metal that then sheds in chips, often asymmetrically, spoiling accuracy. This is why setting a barrel back and re-cutting the chamber works. But lapping is not asymmetric and it affects the whole length of the bore. So, does it remove metal and does throat wear remove metal? Yes. But beyond that generalization the resemblance disappears. In particular, for cast bullet shooters who can size bullets to match the new dimensions of their bore, fire lapping is just a method of forming a bore for cast bullets.
 
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