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  #1  
Old 09-02-2008, 05:48 PM
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Question lapping gun barrels


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what is the difference between fire lapping and handlapping barrels and how is hand lapping done?:
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  #2  
Old 09-02-2008, 06:41 PM
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Quote:
Originally Posted by mister c View Post
what is the difference between fire lapping and handlapping barrels and how is hand lapping done?:

Fire Lapping uses slow speed lead bullets coated with abrasives. The bullets lap the entire barrel but cut a little more at first which tends to leave the muzzle smaller which is prefered. You are at the world's foremost fire lapping forum. Beartooth Bullets up at the top of the page has everything you need!

Hand lapping uses a lead slug poured inside the barrel which is removed, coated with abrasive and pushed back and forth through the bore. Works good but is not as forgiving as fire lapping.
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Old 09-03-2008, 04:32 AM
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You can get Marshall's book for information on fire lapping, see the Beartooth site.

I'm not aware of any books for hand lapping, although one of the Gun Digests (or perhaps Handloader's Digests) a few years back had an article by Ed Harris I believe. Try putting some of that in a search engine.
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  #4  
Old 09-03-2008, 08:39 AM
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thanks everyone for the info on cast bullet load and barrel lapping...........mr.c
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  #5  
Old 09-03-2008, 04:54 PM
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Here's an article to start with and MikeG's suggestion to get the Beartooth bullet manual is an excellent one. Marshall has all the material available in a kit to do the firelapping and the book is invaluable if you shoot cast bullets in handgun or rifle.

http://www.beartoothbullets.com/tech...h_notes.htm/48
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  #6  
Old 09-11-2008, 08:25 AM
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What effect does fire lapping have on the chamber?

Can too much fire lapping pose a problem?
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  #7  
Old 09-11-2008, 10:44 AM
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Originally Posted by lumberjak View Post
Hand lapping uses a lead slug poured inside the barrel which is removed, coated with abrasive and pushed back and forth through the bore. Works good but is not as forgiving as fire lapping.
i don't know if i understand what you're saying so let me ask. how is hand lapping not as forgiving as firelapping. and not to get flamed here as i will probably be in the minority but i have read horror stories on folks firelapping and ending up ruining their barrles/throats. is all that hog wash?
all i know is that the really good barrel makers all hand lapp thier barrels, i don't know of one that firelaps or even suggest it. please don't thow me under the bus, i'm just trying to understand it all.
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Old 09-11-2008, 12:26 PM
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Come On Guys.....

......get familiar with your weapon. Show some respect to that gun. Show it you care. Hold it,hug it,"hand" lapp it like I do.

Grab up a well made rod(Tipton for me).
Get the proper jag.
Apply a liberal amount of the "right" polishing compound. I use either JB Cleaner or Rem Clean(#24017). Both are "gritty".
400 pases(up and back is one). 500 would be even better !
Keep the jag tight. You gotta work for the results. When it starts to get a little easy,put on another patch to make it tight.(think...burnishing) You should be going back and forth fast enough and the jag should be tight enough for the bbl to heat up slightly.

Clean thoroughly. Done. Just a hour and a half gone outta your day. Take a look.

I have had people "in the know" look at the bbl after this process,using a bore scope. All have gave the process a thumbs up.

OR........you can get your local gunsmith to do the very same thing and he will charge you $50. ------pruhdlr
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  #9  
Old 09-11-2008, 12:38 PM
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while the tight fitting jag with a patch will polish your bore, i have been under the impression that in order to truely lap your bore you must cast a lead slug as desribed earlier in this post for an exact match to the bore and rifling and then with fine compund lap the entire bore and rifling.
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  #10  
Old 09-11-2008, 01:28 PM
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Quote:
Originally Posted by Jim H View Post
i don't know if i understand what you're saying so let me ask. how is hand lapping not as forgiving as firelapping. and not to get flamed here as i will probably be in the minority but i have read horror stories on folks firelapping and ending up ruining their barrles/throats. is all that hog wash?
all i know is that the really good barrel makers all hand lapp thier barrels, i don't know of one that firelaps or even suggest it. please don't thow me under the bus, i'm just trying to understand it all.
Hope there's room under the bus for both of us! In general, lapping is nothing more than an abrasive grit applied to steel, it simply removes metal. There are horror stories but if we assume a barrel won't shoot, then it would be hard to ruin it. It's up to each individual to decide if he or she can live with the performance they are getting. If a new barrel shoots pretty good, it makes good sense to just shoot it in. It might shoot better and clean easier in a couple hundred rounds. A rough bore or one that has constrictions could take much longer and fire lapping or hand lapping can be a fast way to get it smoothed out. Not all barrel makers agree on any kind of lapping. I think it was Obermeyer who said "you're just wearing out the barrel".

For either process, you need a material that will apply sufficient pressure to make the abrasive bite the steel. A patch wrapped brush or mop will work but it would be a very slow process and tend not to cut the tight spots any more than the rest. It will polish but that's about it. In fire lapping, a lead bullet is fired that is coated with grit. It starts cutting anything it touches the moment it is fired but once it hits a constriction, it will be slightly reduced in size. The next bullet does the same but keep in mind that the constriction is being cut also. During this process, each bullet cuts a little and eventually the constrictions are reduced and all the lands and grooves are smoother. Since fire lapping tends to cut less at the muzzle because of wear on the bullet and abrasive, you should end up with a barrel that cleans easier and shoots better because the constrictions that were sizing your bullet down are gone. Kits for fire lapping like you can get here at BTB have done all the homework for you. You get the correct supplies along with the instructions to do it right.

Hand lapping is pretty simple also. You need something you can push down the barrel with abrasive on it. Again, you need a material that will keep pressure against the grit to cut the steel. If you "feel" a tight spot, you have to work it down at the same time you lapp the lands and grooves and if you enlarge the muzzle by starting at that end, you're barrel will probably not shoot. This is best done with the barrel out of the receiver, it's certainly easier. Though it may be simple and can probably done in a dozen different ways, it takes a little thought about what you're doing hence less forgiving. Once steel is removed, it's gone forever.

I'm leaving out much detail but I hope you understand my opinion in relation to what I said. Might be worth mentioning there are different types of barrels with unique problems. Handgun, rifle, those with slots machined in and those that are smooth.

Just my opinions and if anyone wants to argue, Jim H and I will be under the bus. Your experiences may vary but I've lapped a barrel or two and I have stayed at a Holiday Inn Express.
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  #11  
Old 09-11-2008, 06:58 PM
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well now i am starting to see both pictures here (lumberjack and myself) with firelapping you are sending down a lead bullet that is being expanded into the lands and grooves in the same manner that castinf a lead slug into a bore would do. so yea now i can see where this would truely lap a barrel if everything is right. i had always heard firelapping and all i could think of was fire and abraseive running down the barrel. but in reality we have a bullet (lead slug) being conformed to the inside of the barrel and polishing the rough spots. is that the idea. even so i am still leary about fireing a bullet to do this as i feel i don;t have much control over it after i pull the trigger, but i do have a better understanding of what is truely going on in the process.
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  #12  
Old 09-11-2008, 09:36 PM
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Polishing and lapping need to be distinguished from one another. Polishing just rubbing an abrasive against a surface to reduce roughness, and the abrasive could be carried by cloth, or even just a fluid, like air. Lapping uses abrasive between two solids. This can also be to achieve polish, as in lapidary tumblers smoothing stones, but in our context it is to obtain a fit or shape or dimension. For example, an amateur telescope maker uses a pitch lap with abrasive to shape his glass mirror blank to have a particular desired focal length. Once it has that shape he carefully polishes it to final surface smoothness for maximum clarity of the reflected image after it is silvered.

Hand bore polishing may be done with pretty much any tight patch as Pruhdlr described. Hand bore lapping is done with a fairly pure lead slug, usually cast directly into the barrel as described. Silicone carbide (Carborundum) abrasive of about 320 grit is most commonly used these days, but aluminum oxide (Alundum) may be used and provides a smoother surface because its grains are less sharp. It also takes longer for that reason.

The pure lead slug is cast and pushed slightly out of the the bore and given a registration mark so it can be put back into the bore with the same lands matching the same grooves in the lap. A cleaning rod with a pivoting handle (ball bearing handle is best) is screwed onto it. A lot of workers then take a knife and put grooves like bullet lube grooves into the lap. The lap is then loaded with abrasive by filling those grooves and pressing it onto the surface. The lap is returned to the bore. On the first pass it rubs the surface of the bore at the entry point and until it is necked down by a constriction. Once necked down, inelastic lead does not spring back, so now it only rubs firmly at the constriction itself. A worker makes repeated passes until even the constrictions don't rub, at which point a dowel is put in the far end of the bore and tapped with a hammer to bump the lead back up to bore diameter, and the back and forth stroking is continued. The lap is removed for fresh abrasive from time to time. It is up to the worker to feel when it is necessary to bump the lap back up or to freshen the abrasive. With practice you can basically feel when to bump up or freshen abrasive because it doesn't feel like it is cutting any more. The basic principle is using the inelastic nature of lead to abrade the bore high spots firmly and repeatedly while abrading the wide spots relatively little. In the end you wind up with a straight bore.

The firelapping process is easier to do but was a little more complicated for its inventors to work out. In principle it is the same thing, a slug is fired that is soft enough not to fully expand back after going through a constriction. However,a problem is you can't use the ideally inelastic pure lead for firelapping bullets. That is because the gas pressure would bump them up after passing through constrictions. If that happens, they polish the bore surface but won't favor the constrictions. If the alloy is too hard it is springy and will spring itself back out to wider diameters doing the same thing. Polishing but not correcting constrictions.

The general consensus for firelapping seems to be that a cast alloy with a BHN of 11 is about the best compromise. It still must be fired at very low pressure to minimize any tendency to obturate. This means you could also hand lap with a lap of that hardness, but it would take longer and would be harder to stroke and more difficult to bump up when it became loose. Plain lead is still most effective for hand lapping.

I have never ruined a barrel by firelapping. I have seen the accuracy with jacketed bullets go unchanged by it, but cast bullet accuracy usually improves and cleaning always improves. I re-slug a bore every few rounds to check progress in constriction removal. Once constrictions are gone, I stop. Final polishing is then ready to be done. Marshal has full instructions on that.

I had occasion to lap a number of M1 Garand barrels at one point. In a standard grade, they typically have a constriction length below the lower band position. My slug measurements showed the breech ends wound up around 0.3 to 0.5 thousandths of an inch bigger than the muzzle. The muzzles only widened 0.1 to 0.2 thousandths. The throats, according to the military throat wear gauge, moved forward about 1 thousandth of an inch. Perhaps that gives you some idea what to expect?
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  #13  
Old 09-12-2008, 11:00 AM
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Nick covered it pretty well. My thoughts on it are that there is perhaps more skill involved in the hand lapping process, although more flexibility. For the beginner, especially with just one gun to do, firelapping should have a shorter learning curve with less chance of foul-up.

If you have a few to practice on, like old military barrels, then I wouldn't be afraid to mess with hand lapping.
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  #14  
Old 09-12-2008, 11:32 AM
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Agree with Mike on there being a learning curve. Especially as to checking progress by cleaning and slugging the bore. Slugging is one of those things you just have to do in order to get the feel of it.

AVIVIII asked if the firelapping process can be overdone, and the answer is yes. It won't affect the chamber because you fire from a case and the case protects the chamber from abrasives. If you over-firelap you can widen your bore too much and wear the throat execessively. I've heard of Microgroove barrels and .22 barrels getting their rifling ironed too flat to work well by overzealous fire-lapping. The solution in both cases is not to use the coarsest abrasive in a graded kit on such barrels, but to start with the next finer grade or to use a finer abrasive only, as in Marshal's kit. Slug to check progress and don't lap beyond correcting and polishing the bore surface and you will be fine.

Jim H commented that custom barrel makers hand lap and don't use the firelapping process. Generally, they don't have the option to firelap even if they wanted to. That is because they produce barrel blanks and contoured blanks, so they have no receiver and no chamber cut from which to fire the rounds. Also, with all the bullet preparation and loading and cleaning and slugging involved, firelapping is not normally any quicker than hand lapping. From a production standpoint it probably makes no economic sense.

By the way, I should mention that nobody has ever shown a hand-lapped barrel to be improved by firelapping that I am aware of, except for throat toolmark removal. At least, not for jacketed bullet shooting. It is really just a good way for the average gun owner to improve mass-produced barrels. I have a couple of such barrels I have not firelapped because they already shoot so well I don't want to mess with success. I just settle for having to clean them more frequently than I might otherwise prefer. If you have a barrel that is a tack driver in the first place, I would recommend that same treatment. Don't mess with success.
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  #15  
Old 09-12-2008, 10:48 PM
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Originally Posted by unclenick View Post

a dowel is put in the far end of the bore and tapped with a hammer to bump the lead back up to bore diameter.

In the end you wind up with a straight bore.

?
You've actually done this? It would take a pretty fair swat to swell a lead plug not to mention getting uniform expansion. How do you hold your lapping rod when using the dowel with enough force to keep it from just jumping back?

I don't think it will straighten the bore, it will just follow it. If the bore is crooked, you will end up with a very pretty crooked bore.
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Old 09-13-2008, 07:48 AM
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I meant straighten constrictions. A long bend in the bore requires a barrel straightening setup to bend the whole barrel.

Bumping up pure lead a couple thousandths is pretty easy. It is very soft. Veral Smith actually sells pure lead cast rods for use in place of chamber casting to get throat and bore and freebore dimensions. He just has you hammer a CRS rod from the muzzle against the lead until it fills out and conforms to the chamber. A big hammer and gentle stroke.

It seems to me the last time I did any hand lapping (a decade or so back) that I inserted a piece of 1/4" brass rod through the bolt channel that reached a wide spot in the bore, and with the gun muzzle up, I struck the rod several times with a 2 lb hammer to bump the slug up. The weight of the cleaning rod attached to the slug and coming out the muzzle end had enough inertia to work against to complete the bumping. You are only looking for two or three thousandths, worst case. Half a thousandth or so is more typical to go from a constriction to a wide spot diameter.
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Last edited by unclenick; 11-19-2008 at 07:11 PM.
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Old 09-13-2008, 08:43 AM
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We have different experiences with lapping. I've never used more than one lap with the exception of a .50 caliber muzzler that had a very tight spot. I draw the line pretty quick on what "might be" improved and what needs to be replaced. Most of my lapping has been done in experimental mode with only a couple being serious jobs and those were on low cost A&B barrels before I finish chambered, cut and crowned. If your after target grade accuracy, save yourself the headache and just buy a quality barrel that's already lapped. If you're playing with a "shooter" that probably needs a new barrel anyway, lapp away.

I have a phobia about having a hammer in one hand and anything metallic shoved down a barrel. I beat on large machines and farm equipment, I lightly tap on gun related merchandise.
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Old 09-13-2008, 11:57 AM
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I'm not clear what your reference to more than on lap is? Do you mean the firelapping bullets? Or maybe you mean you never needed to bump one back up?

I might be inclined to lap a little further than you are. The military spec for .308 barrels is a groove diameter of 0.3065" to 0.3095", so I always think there is a range to be played with. I know some European shooters actually prefer a slightly wide bore. That is strictly for jacketed bullets, of course. It would be a disaster with undersized lead.

I understand your feeling on the hammer and rod, but brass will have a pretty hard time inflicting damage on a bore. Veral Smith says the CRS can't hurt it either, but I would sure face the rod and radius its corners before trying. I might even make a paper sleeve for it, just to be sure? I use a borescope these days to check firelapping progress and would do the same for hand lapping if I were undertaking that again.
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Old 09-13-2008, 01:35 PM
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Originally Posted by unclenick View Post
I'm not clear what your reference to more than on lap is? Do you mean the firelapping bullets? Or maybe you mean you never needed to bump one back up?
I pour only one lapping slug. One lapping slug will do a good job on most barrels for my purposes. If I felt I needed more, I would pour another slug. I've never heard of anyone bumping up the slug but I'm sure there are many ways to skin this cat and it's not an area I plan on doing much of or take on as a profession. I'm sure it works good for you but you hear a lot of ideas that sound good but don't work in practical application or it's more trouble than it's worth.
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Old 11-19-2008, 09:02 AM
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Old gun w/average barrel

I really have enjoyed this lapping discussion and it got me interested in whether or not such a thing would work on and possibly be beneficial to an "OLD" barrel that might need it (I think). I am talking about a Winchester 1890 .22 short with what appears to be a fairly good bore. I just bought it from a neighbor and he threw in an "OLD" box of .22 shorts with it. I actually plan on restoring, re-bluing, and eventually shooting this rifle (please - no one have a hissy fit and start screaming at me - it's my gun you know ) and my three grandsons can't wait to shoot it too.
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