What is barrel lapping?

aarondhgraham · February 1, 2015, 01:38 PM

What is barrel lapping?

Or rather why does one do it?

I really don't know anything more about the topic than it's name.

I've read that it "polishes" the bore,,,
But when is it appropriate to do it.

Will it help a mildly corroded bore?

I'm truly ignorant about the process,,,
Any explanations on why, when, and how will be appreciated.

Thanks gentlemen,,,

Aarond

.

T. O'Heir · February 1, 2015, 02:05 PM

Same idea as lapping a valve in an engine. Smooths out the surfaces. Machined surfaces are not smooth at the 'wee tiny' level. All of 'em have bumps and uneven parts. Lapping fixes that by taking out very fine tool marks. Does nothing for corrosion though.
Isn't really needed for a hunting rifle. More for high end target barrels.
Literally done with a paste(lapping compound), a cleaning rod and jag.

49willys · February 1, 2015, 02:10 PM

Would it help accuracy in an older barrel?

Jimro · February 1, 2015, 02:53 PM

Would it help accuracy in an older barrel?

No, not really. The biggest reason that barrels lose accuracy is the throat gets worn and the muzzle gets worn. You can pull the barrel, cut off the threads then rechamber. The worn muzzle part doesn't hurt accuracy as long as it can release the bullet uniformly, but eventually it will get so big that gas bypass will get to be a real issue eventually.

You can generally get a rifle to shoot pretty decent (I know, such a highly precise term) as long as you have a good throat and a good muzzle, even if the rifling in between isn't perfectly pristine.

Jimro

HiBC · February 1, 2015, 03:31 PM

As a general shop term,"lapping" is the process of cutting a harder material with grit that embeds in a softer material.That is not a book definition,but I have done considerable lapping in industry.

Often lead,copper,or brass are chosen as the softer material.

Generally,it is desirable for the lap to conform to the geometry of the workpiece.The very best you can do is cut off the high spots of irregularities,reduce the rms of the finish..the altitude difference between the high spots and the low spots.
Another benefit of barrel lapping is getting the "lay" of the surface finish ,the "grain" in loose terms,all going in the direction of the bullet.

You can imagine as a drill or reamer goes through,the marks are pretty much perpendicular to the path of the bullet,like washboard road or file teeth.

The barrel maker generally strives to keep the features of the rifling crisp,as cut,not rounded and washed out.And,it is desirable that the dimensions of the bore are uniform to slightly tapered ,the size reducing from breech to muzzle by a very small amount.Tight spots can be relived via lapping.

I do not know what method is used by modern barrel makers.I tried a method described in the book "Modern Gunsmithing" by Baker,IIRC.

A tapered brass wood screw is fixed to the end of a one piece cleaning rod.A patch is placed on the screw so lead can be cast around the screw inside the bore.This is all inserted from the breech,so the screw just protrudes from the muzzle.Then molten lead is poued in from the muzzle around the screw.The patch plugs it from falling through.
Space limits me from describing the whole process,but from this point on,the lap is not removed from the bore.As it is cast in place,it conforms to the geometry of the bore.Screwing the tapered screw into the lap tightens the lap.

Grit and oil are charged on the lap as it is partially,but never completely,protruded from the barrel.

Generally,the barrel maker is a whole lot better at it than an amateur effort.Generally,ameteur efforts subtract from the life/quality of a barrel ,rather than improve it.

IMO,the time to try lapping is when you figure you have nothing to lose.

Then relax,have fun,see what happens.

Fire lapping is one process an amateur can try.It involves firing bullets embedded with grit.

The bullet is formed to the shape of the bore in the throat,and does cut the "lay" all in the direction of travel.

I did it one time,with very good success on a "bargain" barrel.It was a 2 1/2 MOA metal fouler,with visible reamer and button gall marks at the muzzle.

I used cast lead 30-30 bullets charged with #9 diamond mold polishing paste.I fired about 20.This was a 30-06.After this treatment..this rifle became one of the more accurate in my possession.I won't say MOA,because you probably would not believe me.
Besides,I don't have scientific MOA evaluation for it,but "minute of 250 yd prairie dog" is close.

Now,there is one more activity that some may consider "lapping",but it is not.
That would be using some patch,mop,brush,etc charged with grit in the bore.IMO,the methods are nothing but detructive.Remember,the goal is to increase uniformity,decrease the RMS ,(high to low spot "altitude" change) by knocking off high spots.You cannot do this if your lap does not have its own form.A mop cuts the valleys at the same time it cuts the peaks,and it rounds and washes out the rifling form.It also does nothing to dimensionally uniform the barrel.
Its your barrel,but,IMO,abrasive with brush,mop,or patch is a misguided amateur effort by a person with high hopes.You may well find benchrest shooters that recommend it,but you are unlikely to find a quality barrelmaker that will recommend it.

Dixie Gunsmithing · February 1, 2015, 04:41 PM

Lapping is generally defined as fine finishing of a machined surface. For barrels, you use a fine abrasive grit and oil to smooth the lands and grooves of the rifling from their cut state, to clean up the marks left from the machining/rifling process. This generally helps with accuracy, and lowered pressures in the barrel.

Lapping and honing are close to the same thing, as far as metal working is concerned. You're taking a rough machined piece, and making it much smoother.

HiBC · February 1, 2015, 07:29 PM

Not meaning to nitpik,Dixie,but there are several methods of putting a fine finish on metal that are not lapping ,such as your buffing wheel.
I have put on many fine finishes in mold cavities using stones,brushes,felt,and diamond compound.Non of those are laps.Sometimes I used laps in mold finishing.I have used brass a lot.I have even used packing crate banding to lap the EDM finish out of thin slots in molds used to make ribs and thin walls.The EDM finish will stick the parts in the molds.

I can lap the inside of scope rings with 240 or 320 grit clover and achieve a coarse cross hatch.

I can lap a hole to a larger size using a tool called a "barrel lap" but it has nothing to do with rifle barrels,it has to do with the way the tool is made and adjusted,like staves of a barrel.

A really good example of transferring the geometric form of the lapping tool to the workpiece is the lapping plate,which is very flat,and used to transfer that flatness to the workpiece.Have you ever seen a granite surface plate get refinished/recalibrated to a Bureau of Standard spec? I have,a number of times.Its done with cast iron lapping plates and diamond grit.

I have lapped tungsten carbide optic mirrors with .001 brass shim stock charged with diamond,laid on a granite surface plate.I was winging it,spec was .0001 flatness.Boss had bid the job and handed it to me.Customer said it was the best he'd ever been able to get.They are in a satellite right now.

But I could lap a gasket sealing surface on a casting with 220 grit.

Surface finish is a component of lapping,but so is geometric form.

Properly applied,lapping can give both.

aarondhgraham · February 2, 2015, 01:00 PM

Thanks gentlemen,,,

I was thinking about a rifle I passed on recently,,,
It was a Winchester Model 67 single-shot 22.

The exterior was in great shape,,,
But the bore was a bit pitted.

I was wondering if lapping the bore by hand (mop and rod) would help it.

But now that I have read your comments,,,
That's probably beyond my skills,,,
And wouldn't do much good.

Thanks for the info gentlemen.

Aarond

.

Dixie Gunsmithing · February 2, 2015, 01:10 PM

With pitting, I doubt it, as it may be too deep. However, you can have the barrel bored and relined with a .22 cal liner. These are used by drilling out the old rifling, using a piloted 3/8" bit, which is the same as the OD of the liner. The liner is then epoxied or soldered into the barrel, trimmed, crowned, and chambered. Some have done these at home, but if you want it soldered, etc., I'd suggest a Gunsmith.

tobnpr · February 2, 2015, 01:53 PM

JB Bore Paste is worth a shot, might get a you a bit of improvement.

Gunplummer · February 6, 2015, 02:45 AM

I have found that with pitting, it is better to fill than remove. The newer .22's should do this, but I am not sure. It works on high power barrels. Just stop using a brush and only clean with a rag. Let the copper fill the pits. I have had some military bores that were horrendous looking and they shot OK. Some I am sure were exposed to salt water to get that bad.

Bart B. · February 7, 2015, 09:36 AM

That .22 rimfire barrel won't have any copper jacketed bullets fired in it to eventually fill the pits in the bore.

Some old rimfire barrels have been bored out then a cold "liner" pushed in a heated barrel for a shrink fit when it reaches ambient temperature. They're glued in now. Expensive, but it does restore the accuracy the rifle had without changing its outside appearance.

http://www.brownells.com/gunsmith-to...prod10974.aspx

Gunplummer · February 7, 2015, 09:42 AM

Not a .22 shooter, but there is some kind of coating on the bullets now. Either way, let the lead fill it in. Worked on my slug barrel. Actually quite cheap to line a barrel, even if you solder it in.

Bart B. · February 7, 2015, 11:31 AM

Soldering in a barrel liner won't damage the barrel's metalurgy properties? I'd think the barrel would have to be heated to 600 or 700 degrees F to melt and flow the solder. Maybe that won't hurt the metal.

Both standard velocity and high speed .22 rimfire ammo has a peak pressure of 24,000 psi average; more than .38 special ammo.

Gunplummer · February 7, 2015, 06:22 PM

Not sure where the last post came from, but no, soldering will not damage the barrel. Most older .22 barrels were cheaper steel anyway. 1117 comes to mind as a popular steel for .22's. If you ever tried to knock a sight base off a Mauser barrel without heating, you will gain a whole new respect for soft solder.

Dixie Gunsmithing · February 7, 2015, 07:08 PM

No, soft soldering a liner wont hurt the barrel, especially it being a .22. One can sweat both ends and have it hold, I always thought, better than epoxy. It's just a matter of cleaning and tinning both the barrel and liner, before applying heat at either end until the solder flows.

I've seen some re-lines that used some shallow grooves turned on the liner, and matching grooves in the new bore. The solder or epoxy in the grooves keyed the liner in place. The grooves were no more than maybe 0.002" deep at each end. I don't think one really needs this for a .22 though.

**Unclenick** · February 9, 2015, 09:43 AM

Bart had the right melt temperatures for bullet casting alloys, but most lead solder alloys have a lot more tin and typically melt below 500°F. One of my favorite soft solders is also one of the strongest lead solder alloys. That is 2% silver added to 63:37 eutectic solder, giving you Sn62Pb36Ag2 solder. This melts at 353°F.

February 1, 2015, 01:38 PM	#1
aarondhgraham Senior Member Join Date: December 1, 2009 Location: Stillwater, OKlahoma Posts: 8,638	What is barrel lapping? What is barrel lapping? Or rather why does one do it? I really don't know anything more about the topic than it's name. I've read that it "polishes" the bore,,, But when is it appropriate to do it. Will it help a mildly corroded bore? I'm truly ignorant about the process,,, Any explanations on why, when, and how will be appreciated. Thanks gentlemen,,, Aarond . __________________ Never ever give an enemy the advantage of a verbal threat. Caje: The coward dies a thousand times, the brave only once. Kirby: That's about all it takes, ain't it? Aarond is good,,, Aarond is wise,,, Always trust Aarond! (most of the time)

February 1, 2015, 02:05 PM	#2
T. O'Heir Senior Member Join Date: February 13, 2002 Location: Canada Posts: 12,453	Same idea as lapping a valve in an engine. Smooths out the surfaces. Machined surfaces are not smooth at the 'wee tiny' level. All of 'em have bumps and uneven parts. Lapping fixes that by taking out very fine tool marks. Does nothing for corrosion though. Isn't really needed for a hunting rifle. More for high end target barrels. Literally done with a paste(lapping compound), a cleaning rod and jag. __________________ Spelling and grammar count!

February 1, 2015, 02:53 PM	#4
Jimro Senior Member Join Date: October 18, 2006 Posts: 7,097	Would it help accuracy in an older barrel? No, not really. The biggest reason that barrels lose accuracy is the throat gets worn and the muzzle gets worn. You can pull the barrel, cut off the threads then rechamber. The worn muzzle part doesn't hurt accuracy as long as it can release the bullet uniformly, but eventually it will get so big that gas bypass will get to be a real issue eventually. You can generally get a rifle to shoot pretty decent (I know, such a highly precise term) as long as you have a good throat and a good muzzle, even if the rifling in between isn't perfectly pristine. Jimro __________________ Machine guns are awesome until you have to carry one.

February 1, 2015, 03:31 PM	#5
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,286	As a general shop term,"lapping" is the process of cutting a harder material with grit that embeds in a softer material.That is not a book definition,but I have done considerable lapping in industry. Often lead,copper,or brass are chosen as the softer material. Generally,it is desirable for the lap to conform to the geometry of the workpiece.The very best you can do is cut off the high spots of irregularities,reduce the rms of the finish..the altitude difference between the high spots and the low spots. Another benefit of barrel lapping is getting the "lay" of the surface finish ,the "grain" in loose terms,all going in the direction of the bullet. You can imagine as a drill or reamer goes through,the marks are pretty much perpendicular to the path of the bullet,like washboard road or file teeth. The barrel maker generally strives to keep the features of the rifling crisp,as cut,not rounded and washed out.And,it is desirable that the dimensions of the bore are uniform to slightly tapered ,the size reducing from breech to muzzle by a very small amount.Tight spots can be relived via lapping. I do not know what method is used by modern barrel makers.I tried a method described in the book "Modern Gunsmithing" by Baker,IIRC. A tapered brass wood screw is fixed to the end of a one piece cleaning rod.A patch is placed on the screw so lead can be cast around the screw inside the bore.This is all inserted from the breech,so the screw just protrudes from the muzzle.Then molten lead is poued in from the muzzle around the screw.The patch plugs it from falling through. Space limits me from describing the whole process,but from this point on,the lap is not removed from the bore.As it is cast in place,it conforms to the geometry of the bore.Screwing the tapered screw into the lap tightens the lap. Grit and oil are charged on the lap as it is partially,but never completely,protruded from the barrel. Generally,the barrel maker is a whole lot better at it than an amateur effort.Generally,ameteur efforts subtract from the life/quality of a barrel ,rather than improve it. IMO,the time to try lapping is when you figure you have nothing to lose. Then relax,have fun,see what happens. Fire lapping is one process an amateur can try.It involves firing bullets embedded with grit. The bullet is formed to the shape of the bore in the throat,and does cut the "lay" all in the direction of travel. I did it one time,with very good success on a "bargain" barrel.It was a 2 1/2 MOA metal fouler,with visible reamer and button gall marks at the muzzle. I used cast lead 30-30 bullets charged with #9 diamond mold polishing paste.I fired about 20.This was a 30-06.After this treatment..this rifle became one of the more accurate in my possession.I won't say MOA,because you probably would not believe me. Besides,I don't have scientific MOA evaluation for it,but "minute of 250 yd prairie dog" is close. Now,there is one more activity that some may consider "lapping",but it is not. That would be using some patch,mop,brush,etc charged with grit in the bore.IMO,the methods are nothing but detructive.Remember,the goal is to increase uniformity,decrease the RMS ,(high to low spot "altitude" change) by knocking off high spots.You cannot do this if your lap does not have its own form.A mop cuts the valleys at the same time it cuts the peaks,and it rounds and washes out the rifling form.It also does nothing to dimensionally uniform the barrel. Its your barrel,but,IMO,abrasive with brush,mop,or patch is a misguided amateur effort by a person with high hopes.You may well find benchrest shooters that recommend it,but you are unlikely to find a quality barrelmaker that will recommend it. Last edited by HiBC; February 1, 2015 at 04:13 PM.

February 2, 2015, 01:00 PM	#8
aarondhgraham Senior Member Join Date: December 1, 2009 Location: Stillwater, OKlahoma Posts: 8,638	Thanks gentlemen,,, Thanks gentlemen,,, I was thinking about a rifle I passed on recently,,, It was a Winchester Model 67 single-shot 22. The exterior was in great shape,,, But the bore was a bit pitted. I was wondering if lapping the bore by hand (mop and rod) would help it. But now that I have read your comments,,, That's probably beyond my skills,,, And wouldn't do much good. Thanks for the info gentlemen. Aarond . __________________ Never ever give an enemy the advantage of a verbal threat. Caje: The coward dies a thousand times, the brave only once. Kirby: That's about all it takes, ain't it? Aarond is good,,, Aarond is wise,,, Always trust Aarond! (most of the time)

February 1, 2015, 02:10 PM	#3
49willys Senior Member Join Date: March 18, 2010 Posts: 158	Would it help accuracy in an older barrel?

February 1, 2015, 04:41 PM	#6
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	Lapping is generally defined as fine finishing of a machined surface. For barrels, you use a fine abrasive grit and oil to smooth the lands and grooves of the rifling from their cut state, to clean up the marks left from the machining/rifling process. This generally helps with accuracy, and lowered pressures in the barrel. Lapping and honing are close to the same thing, as far as metal working is concerned. You're taking a rough machined piece, and making it much smoother.

February 1, 2015, 07:29 PM	#7
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,286	Not meaning to nitpik,Dixie,but there are several methods of putting a fine finish on metal that are not lapping ,such as your buffing wheel. I have put on many fine finishes in mold cavities using stones,brushes,felt,and diamond compound.Non of those are laps.Sometimes I used laps in mold finishing.I have used brass a lot.I have even used packing crate banding to lap the EDM finish out of thin slots in molds used to make ribs and thin walls.The EDM finish will stick the parts in the molds. I can lap the inside of scope rings with 240 or 320 grit clover and achieve a coarse cross hatch. I can lap a hole to a larger size using a tool called a "barrel lap" but it has nothing to do with rifle barrels,it has to do with the way the tool is made and adjusted,like staves of a barrel. A really good example of transferring the geometric form of the lapping tool to the workpiece is the lapping plate,which is very flat,and used to transfer that flatness to the workpiece.Have you ever seen a granite surface plate get refinished/recalibrated to a Bureau of Standard spec? I have,a number of times.Its done with cast iron lapping plates and diamond grit. I have lapped tungsten carbide optic mirrors with .001 brass shim stock charged with diamond,laid on a granite surface plate.I was winging it,spec was .0001 flatness.Boss had bid the job and handed it to me.Customer said it was the best he'd ever been able to get.They are in a satellite right now. But I could lap a gasket sealing surface on a casting with 220 grit. Surface finish is a component of lapping,but so is geometric form. Properly applied,lapping can give both.

February 2, 2015, 01:10 PM	#9
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	With pitting, I doubt it, as it may be too deep. However, you can have the barrel bored and relined with a .22 cal liner. These are used by drilling out the old rifling, using a piloted 3/8" bit, which is the same as the OD of the liner. The liner is then epoxied or soldered into the barrel, trimmed, crowned, and chambered. Some have done these at home, but if you want it soldered, etc., I'd suggest a Gunsmith.

February 2, 2015, 01:53 PM	#10
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	JB Bore Paste is worth a shot, might get a you a bit of improvement. __________________ Remington 700/Savage Rebarreling /Action Blueprinting 07 FFL /Mosin-Nagant Custom Shop/Bent Bolts Genuine Cerakote Applicator www.biggorillagunworks.com

February 6, 2015, 02:45 AM	#11
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	I have found that with pitting, it is better to fill than remove. The newer .22's should do this, but I am not sure. It works on high power barrels. Just stop using a brush and only clean with a rag. Let the copper fill the pits. I have had some military bores that were horrendous looking and they shot OK. Some I am sure were exposed to salt water to get that bad.

February 7, 2015, 09:36 AM	#12
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	That .22 rimfire barrel won't have any copper jacketed bullets fired in it to eventually fill the pits in the bore. Some old rimfire barrels have been bored out then a cold "liner" pushed in a heated barrel for a shrink fit when it reaches ambient temperature. They're glued in now. Expensive, but it does restore the accuracy the rifle had without changing its outside appearance. http://www.brownells.com/gunsmith-to...prod10974.aspx

February 7, 2015, 09:42 AM	#13
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	Not a .22 shooter, but there is some kind of coating on the bullets now. Either way, let the lead fill it in. Worked on my slug barrel. Actually quite cheap to line a barrel, even if you solder it in.

February 7, 2015, 11:31 AM	#14
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Soldering in a barrel liner won't damage the barrel's metalurgy properties? I'd think the barrel would have to be heated to 600 or 700 degrees F to melt and flow the solder. Maybe that won't hurt the metal. Both standard velocity and high speed .22 rimfire ammo has a peak pressure of 24,000 psi average; more than .38 special ammo. Last edited by Bart B.; February 7, 2015 at 11:38 AM.

February 7, 2015, 06:22 PM	#15
Gunplummer Senior Member Join Date: March 11, 2010 Location: South East Pa. Posts: 3,364	Not sure where the last post came from, but no, soldering will not damage the barrel. Most older .22 barrels were cheaper steel anyway. 1117 comes to mind as a popular steel for .22's. If you ever tried to knock a sight base off a Mauser barrel without heating, you will gain a whole new respect for soft solder.

February 7, 2015, 07:08 PM	#16
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	No, soft soldering a liner wont hurt the barrel, especially it being a .22. One can sweat both ends and have it hold, I always thought, better than epoxy. It's just a matter of cleaning and tinning both the barrel and liner, before applying heat at either end until the solder flows. I've seen some re-lines that used some shallow grooves turned on the liner, and matching grooves in the new bore. The solder or epoxy in the grooves keyed the liner in place. The grooves were no more than maybe 0.002" deep at each end. I don't think one really needs this for a .22 though.

February 9, 2015, 09:43 AM	#17
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Bart had the right melt temperatures for bullet casting alloys, but most lead solder alloys have a lot more tin and typically melt below 500°F. One of my favorite soft solders is also one of the strongest lead solder alloys. That is 2% silver added to 63:37 eutectic solder, giving you Sn62Pb36Ag2 solder. This melts at 353°F. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle