My apologies for not taking notes last time this topic came up.

What is the technique for polishing (lapping) a barrel with a lead lap? Starting from the beginning.

I'm curious, so I have a factory barrel to compare the appearance of the interior finish before and after lapping (e.g. borescope, lap, re-borescope).

Thanks in advance.

LD

Damn it LD, I thought this had to do with technique for ice cream or something more exotic...... like caramel apples.

See if you can find something here: https://forums.accuratereloading.com/eve/forums?a=se...&forum_scope=9411043

quote:

Damn it LD, I thought this had to do with technique for ice cream or something more exotic...... like caramel apples.

Chic,
Lois is comissar of the directorate of lapping in this neck of the woods .

Malm,
Thanks.

quote:

My apologies for not taking notes last time this topic came up.

What is the technique for polishing (lapping) a barrel with a lead lap? Starting from the beginning.

I'm curious, so I have a factory barrel to compare the appearance of the interior finish before and after lapping (e.g. borescope, lap, re-borescope).

Thanks in advance.

LD

One technique for systematic lapping is:
you put a straight steelrod with a stoppingmaterial apx 6" from the rodend in the barrel from the muzzelend so it just stops at the chamberend, then you pump melted lead (i prefere ten) up the barrel to make a perfect cast of the rifeling.
Then you place the barrel in a ficture upwards with chamberend pointing down over a small toples bottel containing a micture of oil greace and grit 220 caborundum .
Then you start pushing the lap 90% out of the chamberend dipping down the compound, then pulling the rood upwards until the lap is 80% out of the muzzle, then downwards, repeating this procedure apx 200 times.
after this you decrease the upwards stroke, turning just when the top of the lap is seen in the muzzle, this you do apx 75 times.(if you are an lazy bastard like me you put on a hydraulic plc controled equipment to do the work, just to prevent you from getting arms like popeyr the sailor)
then you take the barrel out of the ficture, and pushes the lapping rood completely out of the chamberend.

Now you have a barrel that according to surfacestraightnes is perfect, both in grooves, on the lands, and in the twistrate(side of the lands) And as a lifetimeprolonging sideeffect it is slightly tapered towards the muzzle
This slight tapering gives you apx 50% longer lifetime and a much higher tolerens for fouling. In many cases you also have a barrel with less friction, that potentialy within the same preasurerange can give you higher velocity.

When looking tru a borescope you might se a surface that does not look so glossy as before, but it has microgroowes from the lappingcompound, but they all runs in the same direction as the bullet shall trawel

Thank you Jorgen,

I like the idea of using a hydraulic arm to do the work. My kids are all grown and gone, otherwise they could get the exercise from lapping the barrels .

LD

220 grit!!

John

About 180-220 grit on a match barrel
Butch

Yes grit 220

The reason for the relativ coarse grit is a theory about friction and contactsurface.

Two surfaces where the one is mirror finished highly polished, combined with an relativ soft mooving part with no lubrication betwen,has a tendency to what i call "sticking". In rifleterms that meens that the soft bulletmaterial sticks to the smooth barrel, resulting in foulign.

When lapped with coars grain the contactarea is redused, and the sticking problem is also reduced, resulting in mutch less fouling. It is not a bad idea to lightly polish the coarse lapped barrel with werry fine steelwoll, Scotchbrite, og Gold medalion, just to take the agressive of the "microrifling" created by the lapping

I am sorry, I thought this thread was about lapping the inside of the barrel, I see we are talking about the outside. I go through about 1000 SS barrels a year, and yes, scotchbrite is a great way to clean up little scratches and such on the outside of the barrel.

All the barrels I buy are match grade barrels so maybe these more barbaric techniques are sometimes usefull on the inside of lower cost barrels. I have a feeling that if I told Krieger that I used steel wool or scotchbrite on the inside of one of my barrels they would probably not stand behind it if there was a problem.

John

John, you may be supprised. I would bet a nickel to a donut that they lap at no finer than 220 on their best match barrels. Jorgen knows what he is talking about.
Butch

quote:

Originally posted by jørgen:
Yes grit 220

The reason for the relativ coarse grit is a theory about friction and contactsurface.

Two surfaces where the one is mirror finished highly polished, combined with an relativ soft mooving part with no lubrication betwen,has a tendency to what i call "sticking". In rifleterms that meens that the soft bulletmaterial sticks to the smooth barrel, resulting in foulign.

When lapped with coars grain the contactarea is redused, and the sticking problem is also reduced, resulting in mutch less fouling. It is not a bad idea to lightly polish the coarse lapped barrel with werry fine steelwoll, Scotchbrite, og Gold medalion, just to take the agressive of the "microrifling" created by the lapping

All of my barrels came from the makers with hand lapped mirror finishes in the bores and all of them clean like a breeze with little or no fouling and/or copper build up. How do you explain that in light of your “theory?â€

I don’t know the answer to this, so lets see if I’m alone.

What degree of roughness (smoothness), measured by the industry standard microinch (one millionth of an inch), could you achieve by using 220 grit lapping/polishing medium?

Shhhhhhh! Be quiet, I think they‘re off looking that one up somewhere!

I have been guided through Shilen's facilities three times. Once in the 1970s when Ed Shilen graciously showed myself and two others through. Once in the 1980s when his son Doug took me through. Once about 1997 when the production manager took myself and another gunsmith through.

I took advantage of every minute I could to see every operation possible and asked a thousand and one questions. Being a gunsmith and interested in accuracy one of the areas that I was keenly interested in learning all I could was barrel lapping. Reading about it and even knowing how is one thing but experiencing it is the bottom line. I knew if I could learn these techniques that I could benefit greatly in my many quests for accuracy.

It turns out I was correct, over the years my customers and myself have benefited greatly from my ability to hand lap barrels both to correct problems and also to enhance performance. But I digress. Back to the subject.

Ed Shilen himself said they only used one grit to lap with..............240 grit. When I questioned not going finer he replied that any finer would cause jacketed bullets to "smear" thereby inviting fouling.

As for Rick observing a "mirror" finish in his barrels. A 240 grit and 220 grit lapped bore too will appear to have a mirror finish to the naked eye. When you use a 20X bore scope you will then see the lap marks. Even under 20X magnification it will have the appearance of perhaps 320 or 400. It looks very smooth. This is due in part to the abrasive breaking down into finer grit particles.

I have an AR-15 match rifle set up for NRA highpower competition. The barrel for it had some pretty serious tool marks in it. So I hand lapped it with 240 grit abrasive. Now when I shoot a match which involves firing over 90 rounds, several strings shot in rapid fire sequence, I come home, run a brush and solvent 10 strokes, patch it, then brush and solvent 10 strokes again and patch it and it is clean. That is clean to the eye of a 20 X bore scope.

I was also concerned about the barrel's ability to group near the end of the match. So I have purposely left it dirty (90 rounds), added a 12 power scope and fired 3/4 inch TEN shot groups over sand bags at 100 yards. Pretty good testimony for 240 grit lapping.

The reason I asked the question was that Krieger barrels are finished to a 16 micro-inch finish...which according to my copy of Machinery’s handbook 25 is a fairly fine finish.

It ain’t like glass, but I just didn’t know if you could go that smooth with 220 grit compound, that’s why I asked the question. Since no one here seems to know the answer I’ll call Krieger tomorrow and ask what they use to get that degree of finish.

quote:

I am sorry, I thought this thread was about lapping the inside of the barrel, I see we are talking about the outside. I go through about 1000 SS barrels a year, and yes, scotchbrite is a great way to clean up little scratches and such on the outside of the barrel.

All the barrels I buy are match grade barrels so maybe these more barbaric techniques are sometimes usefull on the inside of lower cost barrels. I have a feeling that if I told Krieger that I used steel wool or scotchbrite on the inside of one of my barrels they would probably not stand behind it if there was a problem.

John

Sorry John
I forgot that you folks over there like to sell SS barrels (is it because of the easier tooling, and mutch shorter lifetime
Of cause you must not use steelwoll in or on a SS barrel, because it can make the SS begin to rust heavily, and it might also be to tough on the relative soft SS. When i talk about barrels i mean CroMo barrels at a hardnes of 29-30Hrc. Mainly produced for 200 and 300m UIT competition, where fouling and lifetime of the harrel is a major issue, because many competitions reqires up to 150 rounds, without chances to remowe fouling. It is not unusual that after 150 rounds they produce 1½" 10rounds at 300meters

Called Kreieger just a bit ago and the lapping compound they use is their own mixture that is allot finer than 220 grit after it is made up, according to the gentleman I spoke with.

As was pointed out by others on here, my using the term “mirror†finish was incorrect because, as was also pointed out, a true mirror finish increases friction.

quote:

Originally posted by Rick 0311:
Called Kreieger just a bit ago and the lapping compound they use is their own mixture that is allot finer than 220 grit after it is made up, according to the gentleman I spoke with.

As was pointed out by others on here, my using the term “mirror†finish was incorrect because, as was also pointed out, a true mirror finish increases friction.

Sorry Rick 0311
No doubt about that Krieger makes superb barrels. But as i say there are several opinions about how to do it.
I presonally dont know the rouhness code on a surface produced by lapping with gritt 220. But in some ways you can look at it as a railway. Preatty bumpy to cross, but werry smooth to ride along.

The advantages by lapping as earlier discribed
Liniery levelling of all internal surfaces (in growes on lands and on the sides of the lands)
Removing reamermarks and chatter
correcting and checking twistrate variations along the barrel
Reducing fouling of importance
By the light chocking of the muzzel increased lifetime, and less sencibility to fouling.

I dont know any measuringteckniques that can document all of it.
I only know that feks airgauging only shows uniformity in hole area, not diameter, nor concentricity or liniary straightness.
Borescope inspection shows surfacequality, but still not straightness or twistrate uniformity.

I have tried to cast those long ten laps in Buttonrifled barrels, sold as select matchquality, and in more than 30% the long lap was impossible to mowe by hand, when remowed by force ther was clear sighns (glossy and compressed spots) of variating twist, excentricity betwen lands and growes and liniary unstraightness

Interesting discussion of lapping...however I am
surprized no one mentioned the subject of "fire lapping" with lap impregnated bullets.
There is a kit endorsed by David Tubbs with lap charged bullets you fire through the rifle..
I also used to lap with soft lead bullets with lap compund in the lead bullet's lube grooves (instead of lube) at lowest possible velocity..
It has worked for me.
Comments?
Best Regards, Tom

quote:

Originally posted by jørgen:
Sorry Rick 0311
No doubt about that Krieger makes superb barrels. But as i say there are several opinions about how to do it.

Sorry about what...and different opinions on doing what?

You lost me on some of this stuff about button rifled barrels, since Krieger’s (the ones I mentioned) are cut rifled.

As I’m sure you know, button rifling is much more difficult to do and keep the twist rate consistent and also to maintain uniformity through the entire length. That’s one of the reasons that button riflers have all the different “grades“ they sell. They can’t make a certain grade “on purposeâ€...that’s just the way they come out.

I think you would probably agree that there is a big difference between the final lapping done by the manufacturer on a new, never used barrel, and that which guys do to help restore an old, used barrel?

quote:

Sorry about what...and different opinions on doing what?

You lost me on some of this stuff about button rifled barrels, since Krieger’s (the ones I mentioned) are cut rifled.

As I’m sure you know, button rifling is much more difficult to do and keep the twist rate consistent and also to maintain uniformity through the entire length. That’s one of the reasons that button riflers have all the different “grades“ they sell. They can’t make a certain grade “on purposeâ€...that’s just the way they come out.

I think you would probably agree that there is a big difference between the final lapping done by the manufacturer on a new, never used barrel, and that which guys do to help restore an old, used barrel?

Rick 0311

What i ment was that even if Krieger (who as earlier mentioned makes superb barrels) meens that one should lap with finer grit it doesnt meen that it is the only truth, but it is surely 1 of them, as diferent uses for barrels might require different lappingtecniques and grits. Also might different materials SS/CroMo require different treatments.

According to what i have seen buttonrifeling is much easier to do, and also far cheaper, but i have to agre that the quality often variates more than whats seen from top cutrifeling producers.

So i guess that when you buy buttonrifeled and hammerforged barrels, of high grade, you pay just as mutch for the measuring and guessingcontrol as for the production it selves, and when you buy quality cutrifled barrels you pay most monney for the production and less for the inspection(whitch in my opinion doesnt ad anny quality it just might clarify the extence of the damages ). On the other hand you find also both god and bad cutrifeling companies
My point about measuringtecniques was just to say that it is in my opinion wery dificult to measure if a barrel is good or less good. And not at all hat anything to do with Kriegers fine barrels.

I totally agre on your last comment about original lapping and "repairlapping" .

The most importent in all barreltreatment, is that the muzzel must never becom bigger than any point in the rest od the barrel

I didn’t say, nor did Kreiger say, that their way was the “only†proper way to lap a barrel, or that what they use is what everyone should be using They only stated what they used in their barrels.

I own Schneider and Shilen barrels (button rifled) as well as Kriegers (cut rifled). Gary’s barrels are all stainless steel, but I have both CM and Stainless Shilen and Kriegers and they all exhibit the same high quality, accuracy, lack of fouling, ease of cleaning, and wearing ability.