Bore lapping

[Hannibal]

There is no shortage of contradictory information on this subject. On everything from what grit/grits to use to how to bump up the lap.

On one hand, I've been told that when using poured laps, never allow them to exit the barrel. And if it does, discard it and pour a new lap as it's not possible to get it indexed back to the same land/groove position from whence it came. And I've also been told as the goal is to make the bore as even as possible, albeit with a slight taper to the muzzle, that lap/land/groove orientation is of no concern.

I've not allowed the lap to leave the barrel until I wanted to pour a new lap thus far. Do any of you who follow the 'non-oriented' method?

Thanks in advance for any advice.

[lefty o]

in short if you want a hand lapped barrel, buy one. after lapping, a barrel truly needs both ends cut off.

[country gent]

I was taught when lapping a barrel to make 3-5 passes rotate 1 groove 3-5 passes for a full rotation. then a new lap and finer grit repeat. to put taper in a barrel 2 passes 3" 2passes to 6" 2 passes to 9" till just out of barrel and repeat with finer grit. With most barrels there is nothing left to lap left in the bore and you end up with an oversized bore. The lapps we poured were 2" long and on a small machine screw then a nut could be used to expand them if needed. a stop was set outside of muzzle and at back of rod to limit travel as needed.
Lapping is messy work. The last one I did I did in a vise standing up right with a block on the floor to limit travel forward and was carefull to not pull it out of the bore on the up stroke.I prefer a set up where I can get straight behind the rod and push it as straight as possible

[Jedman]

I lapped a 45-70 barrel once that had a few tight spots along its length. The way I did it was I took a long lead 45 cal. bullet that had 3 lube grooves and pounded it thru the bore like slugging it.
Then I drilled a hole length wise thru the bullet for a 8/ 32 or 10/ 32 screw to screw into a cleaning rod. I scraped the lube out of the bullet grooves and filled them with 400 grit valve grinding paste and pushed it back and forth many times thru the tight spots and quit when it felt like all the same effort from breech to muzzle.

It did help a lot ! It not only was more accurate but also fowled much less.

Jedman

[Hannibal]

in short if you want a hand lapped barrel, buy one. after lapping, a barrel truly needs both ends cut off.

While this is quite correct, I've nothing to learn this way. I understand most 'smiths, and shooters as well, just want an accurate rifle by the simplest and least complicated means.
I have a few damaged barrels, and an inquiring mind. So please indulge my experimenting, if you would.

Thank you for the advice.

[Hannibal]

I lapped a .357 Henry that had tight spots at all the dovetails. Did it while it was attached to the receiver because I couldn't find any information about barrel removal and I didn't want to muck it up. I used 400 grit lapping compound and laps poured around a3"piece of all-thread. I forget the size now. 8-32 I think. While it didn't turn it into a benchrest rifle by any stretch of the imagination, it DID make a SIGNIFICANT improvement.

I have a .223 barrel with a hideously coarse bore I'd like to lap next. It doesn't group, it 'patterns', so there's nothing to lose but some time and sweat. What I will gain is a question yet to be answered. Given that the bore is so much smaller, obviously, this will be more challenging.

[john.k]

A lap should be charged with abrasive and then have the loose abrasive washed off.Loose abrasive causes bellmouthing .A charged lap will not wear the ends any more than any other place,provided that correct lapping practice is followed.Stirring abrasive slurry with a piece of lead is not lapping.Any old book on toolmaking will have the requirements .Lapping is very useful for restoring blackpowder barrels where an increased diameter can be tolerated.For instance I recently lapped a 450 barrel to eliminate pitting,and it now uses 476 bullets cast in a cheap lee mold.

[lefty o]

While this is quite correct, I've nothing to learn this way. I understand most 'smiths, and shooters as well, just want an accurate rifle by the simplest and least complicated means.
I have a few damaged barrels, and an inquiring mind. So please indulge my experimenting, if you would.

Thank you for the advice.

by all means, have at it. especially if you have some damaged barrels.

[Hannibal]

A lap should be charged with abrasive and then have the loose abrasive washed off.Loose abrasive causes bellmouthing .A charged lap will not wear the ends any more than any other place,provided that correct lapping practice is followed.Stirring abrasive slurry with a piece of lead is not lapping.Any old book on toolmaking will have the requirements .Lapping is very useful for restoring blackpowder barrels where an increased diameter can be tolerated.For instance I recently lapped a 450 barrel to eliminate pitting,and it now uses 476 bullets cast in a cheap lee mold.

I think I understand what you are saying, but how do you propose to charge the grooves of the lap, which obviously will be the area contacting the lands on the bore. I've heard of rolling slugs between steel plates, but once the slug is driven into the bore, it seems to me that the abrasive will not be present in the newly formed grooves on the slug, or am I missing my guess?
Perhaps there is a method of embedding the abrasive I've not heard of or considered? Can you explain a bit further?
Thanks in advance.

[Hannibal]

I was taught when lapping a barrel to make 3-5 passes rotate 1 groove 3-5 passes for a full rotation. then a new lap and finer grit repeat. to put taper in a barrel 2 passes 3" 2passes to 6" 2 passes to 9" till just out of barrel and repeat with finer grit. With most barrels there is nothing left to lap left in the bore and you end up with an oversized bore. The lapps we poured were 2" long and on a small machine screw then a nut could be used to expand them if needed. a stop was set outside of muzzle and at back of rod to limit travel as needed.
Lapping is messy work. The last one I did I did in a vise standing up right with a block on the floor to limit travel forward and was carefull to not pull it out of the bore on the up stroke.I prefer a set up where I can get straight behind the rod and push it as straight as possible

It sounds like the approach was pretty aggressive, unless I'm misreading your reply. Were any attempts ever made at smoothing up a rough, fouling bore? Or were these old, badly damaged barrels, such as mil-sups with corrosion damage? I've not tried anything but 400 grit abrasive thus far. Some have said that is too fine even for final finish, let alone to start with. (?) What grits were employed in the processes you describe, if you recall?

Thank you in advance.

[country gent]

I worked with clover lapping compounds 320 and finer. Not overly aggressive but metal is removed ( a .0002 removed is .0004 on dia). Rotating the lap helps to keep lands and groove even .
To charge the lap roll between to flat steel plates with mild to semi heavy pressure thru the compound and wipe excess off .

In lapping the soft material is charged or impregnated with the compound and becomes a "precision file" for lack of a better term. It then cuts the harder material. The lead slug is the carrier for the abrasive which is harder than the steel. Once impregnated with a grit the lapp is that, a new lapp needs to be Impregnated with finer grits. The longer lapps carry more grit and more surface giving a better more precise job. Also light oil helps with the cutting and finish

The barrels I did were slightly under sized and rough they had some room to work with. Removing more than .001 - .002 is a lot of work but as above that's .002 to .004 on dia.

[Hannibal]

I worked with clover lapping compounds 320 and finer. Not overly aggressive but metal is removed ( a .0002 removed is .0004 on dia). Rotating the lap helps to keep lands and groove even .
To charge the lap roll between to flat steel plates with mild to semi heavy pressure thru the compound and wipe excess off .

In lapping the soft material is charged or impregnated with the compound and becomes a "precision file" for lack of a better term. It then cuts the harder material. The lead slug is the carrier for the abrasive which is harder than the steel. Once impregnated with a grit the lapp is that, a new lapp needs to be Impregnated with finer grits. The longer lapps carry more grit and more surface giving a better more precise job. Also light oil helps with the cutting and finish

The barrels I did were slightly under sized and rough they had some room to work with. Removing more than .001 - .002 is a lot of work but as above that's .002 to .004 on dia.

Ok, I think I understand. Thank you for the additional information.

[john.k]

The abrasive is charged into grooves with a small ,narrow roller in a handle.Nowdays,far more aggresive materials are available,such as pol/c diamond and CBN,and cut far better than the traditional grits.In fact,when you get a bit of experience ,you can make laps for the bore only,and for the grooves only.With the hard materials much harder laps are usable,and Ive been using the Cerro metals,which have very low melting point.Not expandable like lead ,tho,but easy to cast..Its most important that laps be kept flooded with cutting fluid to stop blinding or stripping of the grit,never let a lap run dry.Power lapping is much easier than manual.

[fiberoptik]

Power lapping?


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[Hannibal]

The abrasive is charged into grooves with a small ,narrow roller in a handle.Nowdays,far more aggresive materials are available,such as pol/c diamond and CBN,and cut far better than the traditional grits.In fact,when you get a bit of experience ,you can make laps for the bore only,and for the grooves only.With the hard materials much harder laps are usable,and Ive been using the Cerro metals,which have very low melting point.Not expandable like lead ,tho,but easy to cast..Its most important that laps be kept flooded with cutting fluid to stop blinding or stripping of the grit,never let a lap run dry.Power lapping is much easier than manual.

What is 'power lapping'? I've never heard the term used before . . . ?

And charging the grooves with a roller handle . . . akin to a roller handle for window screen spline?

You've got 'the wheels turning'. Thanks for that!

I see you are from Australia. 'Gunsmiths' here in the US like to place a shroud of mystery on lapping. I intend to change that. We shall see, eh?

[Traffer]

Great thread. Much valuable info. Thanks to the guys who posted. I learned a lot in just a few minutes here.

[Texas by God]

C.E. Harris wrote a good article about how to lap a rifle barrel in the American Rifleman in the nineties I believe.

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[Jim_P]

If the reason you need to lap that barrel is not too much damage, I have fire lapped two barrels. One in 7MM Rem Mag and the other in .308. Improvement was very noticeable. Get Dave Tubbs Final Finish bullet or rounds here: http://www.davidtubb.com/final-finish-loaded-ammo. I also think Midway has them.

If you're just getting out bad copper or lead fouling, start at the middle grade to fine. Same for surface rust. All Five grades for pitting and such.

I will tell you when I did the two I did, they became better shooters. The .308 was used and had some minor pitting, and it did the job with all 5 levels of compound.

Besides, you get to go shooting to do the job. Win-Win in my book. Also, I just put the rounds in the ground. Didn't worry about a target to fire them. Follow the directions and it works!

[Hannibal]

I find the idea of fire lapping intriguing as well. Perhaps the only up side to having several damaged barrels is I get to try several approachs.
Fire lapping is on the list, just not right now with this barrel.

[largom]

If the reason you need to lap that barrel is not too much damage, I have fire lapped two barrels. One in 7MM Rem Mag and the other in .308. Improvement was very noticeable. Get Dave Tubbs Final Finish bullet or rounds here: http://www.davidtubb.com/final-finish-loaded-ammo. I also think Midway has them.

If you're just getting out bad copper or lead fouling, start at the middle grade to fine. Same for surface rust. All Five grades for pitting and such.

I will tell you when I did the two I did, they became better shooters. The .308 was used and had some minor pitting, and it did the job with all 5 levels of compound.

Besides, you get to go shooting to do the job. Win-Win in my book. Also, I just put the rounds in the ground. Didn't worry about a target to fire them. Follow the directions and it works!

I have fire-lapped dozens of barrels with Tubb's Final Finish and every one shot better. Not necessary to always use the full kit on every barrel. The improvement in some barrels was outstanding.
Larry

[longbow]

There does seem to be a lot of mystery and opinions on lapping barrels. Some say all you are doing is wearing out the barrel. I don't buy that at least for cast boolits, and some reasons, like yours, to repair "damage". Better to try lapping than put up with a bad barrel or just toss it.

I am no expert by any means and wouldn't claim I took a bad, mediocre or even just slightly off barrel and made a bench rest shooter out of it. However, I do have a Marlin 1894 that leaded badly and was not very accurate. By using "fat" boolits a little over groove diameter accuracy improved and leading diminished but accuracy was still not great and leading was still a bit of an issue.

Then I read about tight spots under roll stamping in Marlin barrels so slugged it pushing a lubricated slug right through the bore and sure enough 3 or 4 tight spots!

Now this is a Marlin microgroove barrel so not a lot of rifling depth but the gun was not much good so I decided to try lapping it by hand. I thought about fire lapping but elected to have some control because of the obvious tight spots. I wasn't just removing tool marks or burrs so figured hand lapping would allow me to concentrate some at the tight spots. What did I have to lose?

I cast a lap, drilled through and put it on a rod trapped between two nuts. I made a muzzle guide then lapped working on the tight spots first. Once they weren't noticeably tight I stroked from breach to muzzle, first with short strokes near the breech then longer strokes then all the way to the muzzle.

Long story short, it worked and done by a total amateur. The gun is far more accurate now and leading is not an issue.

Would I take a high priced precision barrel and try lapping to make it better? No. In this case and yours why not?

I haven't tried fire lapping but would not hesitate if I had a barrel with tool marks in it or one that didn't shoot as well as it should with no obvious reason. Why shoot hundreds of rounds with mediocre accuracy to break a barrel in?

Longbow

[waksupi]

I fire lapped a Douglas barrel with LBT lapping compound. Low velocity loads for a half dozen shots, clean, test fire again. I had to fire around 18 rounds to get the accuracy where it should be.
When I was cleaning the barrel between trials, I would hear the barrel squeaking as it went down the bore, and then it would stop when I got to the rough part. I could actually hear the progress of the lapping, and when it squeaked all the way, I was done.