“Lapping” rifle barrels?

[CoElkHunter]

Not knowing anything about this subject, I Googled it. Basically, the information I found was the lapping was used to increase accuracy and/or help renew rusted/pitted barrel rifling in older military rifles? What would be the advantage of “lapping” a large bore hunting rifle with good rifling in the bore when MOA accuracy or the potential to “shoot out” the barrel isn’t an issue? Thanks!

 

[nztimb]

No value whatsoever on a bog bore or hunting rifle barrels in general although some makers offer lapped barrels with the cost of doing so added. Lapping was traditionally done to reduce machine marks in the throat and portion closer to the chamber with less done as the lap reached toward the muzzle. It is a long and laborious process necessitating new laps as the job progresses.

 

[Ridgewalker]

CoElkHunter, a number of barrel makers currently lap the barrels, as Von Gruff mentioned it is primarily to smooth out machining lines in the rifling to reduce fouling. Most rifles eventually are lapped if they are shot enough.
Some precision target shooters do it or what they calL “fire lapping”. Some world class precision shooters (David Tubb as an example) have a process where they coat bullets with lapping compound then load them at lower velocities and fire them.
I believe Sako and Tikka barrels are factory machine lapped. Also I understood my MRC In 375 H&H was lapped. I believe them both because they are very easy to clean!

 

[CoElkHunter]

CoElkHunter, a number of barrel makers currently lap the barrels, as Von Gruff mentioned it is primarily to smooth out machining lines in the rifling to reduce fouling. Most rifles eventually are lapped if they are shot enough.
Some precision target shooters do it or what they calL “fire lapping”. Some world class precision shooters (David Tubb as an example) have a process where they coat bullets with lapping compound then load them at lower velocities and fire them.
I believe Sako and Tikka barrels are factory machine lapped. Also I understood my MRC In 375 H&H was lapped. I believe them both because they are very easy to clean!

Interesting? I just thought that something .375 and up wouldn’t need a barrel lapping because they wouldn’t be shot enough to wear out the rifling or need extensive cleaning before they were sold to Toby458? Guess I was wrong again?

 

[Ridgewalker]

Interesting? I just thought that something .375 and up wouldn’t need a barrel lapping because they wouldn’t be shot enough to wear out the rifling or need extensive cleaning before they were sold to Toby458? Guess I was wrong again?

Too too funny!!!

 

[CoElkHunter]

Ok, how about this. Run some very coarse sandpaper through the bore with a cleaning rod a thousand times in concert with working the action of my CZ to smooth it out? Two issues solved simultaneously? THEN, shoot it once and sell it to Toby?

 

[Ridgewalker]

All kidding aside, I have used JB Compound to clean barrels heavily fouled with copper. Maybe as much as 100 strokes. It cleaned the copper fouling and actually seemed to help prevent more excess fouling.

 

[CoElkHunter]

All kidding aside, I have used JB Compound to clean barrels heavily fouled with copper. Maybe as much as 100 strokes. It cleaned the copper fouling and actually seemed to help prevent more excess fouling.

Yes, in more seriousness I’m going to try this. The Barnes bullets I’ve shot tend to “streak” the barrel a bit, but I figure the copper will fill in the microscopic imperfections in the barrel metal and whatever is left after cleaning is not much of a problem in a large bore, close range hunting rifle?

 

[bruce moulds]

first of all, j.b. is nothing to do with lapping.
it is not aggressive enough to lap a barrel.
lapping is done to give guaranteed internal dimensions to a barrel.
it is also to make these dimensions consistent.
ant new barrel will have tighter and looser spots along its length, even those by Krieger and bartlein.
they are a little undersize to allow removal of metal by lapping.
lapping often involves a lead slug impregnated with a coarser than expected abrasive, initially removing the tight spots, then bringing the whole length to full dimension.
they will often lap in up to 4/10 of 1 thou taper, the muzzle end being tighter.
some makers will custom lap a taper to customer spec, within reason.
looking at a custom lapped barrel with a high magnification borescope reveals quite a rough surface, with all the scratches going with the rifling.
this is preferable to a dead smooth surface, which will guarantee to foul badly.
I have lapped a barrel, and the differences between the tight and loose spots was so pronounced that the lap was loose in the looses spots, and could be barely pushed through the tight.
all barrels, whatever the method of manufacture, can benefit from lapping due to dimensional irregularities.
I have a 26:13 gaintwist by ron smith of Canada, and even that can be and was lapped.
laps can be cast in the bore of pure lead which are on a threaded push/pull rod such that a nut on the thread can be tightened to expand the lap as required.
lapping a factory barrel might do all the things you want, but will ruin it due to being over spec in diameter.
same with lapping out pitting.
this does not matter with cast bullets, as you can get a bigger mould, or if patching, uses thicker paper.
I would advise against home lapping, as it is better done by more experienced operators.
the best lapping is all done one direstion, from breech to muzzle.
bruce.

 

[Ridgewalker]

Yes, in more seriousness I’m going to try this. The Barnes bullets I’ve shot tend to “streak” the barrel a bit, but I figure the copper will fill in the microscopic imperfections in the barrel metal and whatever is left after cleaning is not much of a problem in a large bore, close range hunting rifle?

I found with Barnes bullets I get my best accuracy by shooting a couple of fouling shots using other bullets. JME

Tubbs Final Finish:
https://www.davidtubb.com/catalog/v...roduct_information/finalfinish_faqs_sheet.pdf

 

[crs]

Guess I was wrong again?

mmm, you should be used to that by now.

I always thought that "lapping" had to do with auto racing.

 

[375 Ruger Fan]

This is from Krieger's website:

SINGLE-POINT CUT-RIFLING
We rifle all of our barrels using the single-point cut-rifling process. Although our machines are state-of-the-art, the process itself is the oldest and slowest method of rifling a barrel. It’s also the most accurate. The cutter removes approximately .0001 inch, or 1 ten-thousandth of an inch, at each pass, thus taking several hundred passes to rifle a barrel. This method produces almost perfect concentricity between bore and groove, a very uniform twist rate, and induces no stress into the steel that later has to be relieved. Along the same lines, we do absolutely no straightening of our barrels as this would only put stress right back into the steel.

Our barrels are lapped after reaming to remove the tool marks, and then hand-lapped again after rifling. It has been said that if a barrel is cut-rifled correctly, it does not have to be finish lapped, and to some extent this is true. It should not have to be lapped to obtain uniformity of dimensions. This should come from the tooling and procedures used. But there is a slight improvement to the finish achieved by finish lapping, and the lay of the finish is now in the direction of the bullet travel so fouling is greatly reduced, and cleaning is made easier. It takes longer to finish lap, but we do it because it makes a better barrel. We are lapping to finishes under 16 micro-inch in the direction of the bullet travel. In contrast the government requires only a 32 micro-inch finish on its M-14 National Match barrels.

 

[Shootist43]

Lapping and the need for it and or the benefits of it IMHO is dependent on the distances being shot and the level of accuracy required. Custom barrels should have already been lapped at the factory. Production barrels seldom if ever are. Fire Lapping can and has benefited the production barrels of several rifles I'm familiar with. Simply shooting a production hunting rifle should improve its initial accuracy, fire lapping just speeds up the process. I doubt it will do anything to help a rusted and or pitted barrel of an old Military rifle.

 

[CoElkHunter]

Guess I was wrong again?

mmm, you should be used to that by now.

I always thought that "lapping" had to do with auto racing.

Being “wrong again” about many things here on AH, seems to be my mantra. It’s OK though, because the many experts here set me straight before I really screw up! Ha! Ha!

 

[CoElkHunter]

first of all, j.b. is nothing to do with lapping.
it is not aggressive enough to lap a barrel.
lapping is done to give guaranteed internal dimensions to a barrel.
it is also to make these dimensions consistent.
ant new barrel will have tighter and looser spots along its length, even those by Krieger and bartlein.
they are a little undersize to allow removal of metal by lapping.
lapping often involves a lead slug impregnated with a coarser than expected abrasive, initially removing the tight spots, then bringing the whole length to full dimension.
they will often lap in up to 4/10 of 1 thou taper, the muzzle end being tighter.
some makers will custom lap a taper to customer spec, within reason.
looking at a custom lapped barrel with a high magnification borescope reveals quite a rough surface, with all the scratches going with the rifling.
this is preferable to a dead smooth surface, which will guarantee to foul badly.
I have lapped a barrel, and the differences between the tight and loose spots was so pronounced that the lap was loose in the looses spots, and could be barely pushed through the tight.
all barrels, whatever the method of manufacture, can benefit from lapping due to dimensional irregularities.
I have a 26:13 gaintwist by ron smith of Canada, and even that can be and was lapped.
laps can be cast in the bore of pure lead which are on a threaded push/pull rod such that a nut on the thread can be tightened to expand the lap as required.
lapping a factory barrel might do all the things you want, but will ruin it due to being over spec in diameter.
same with lapping out pitting.
this does not matter with cast bullets, as you can get a bigger mould, or if patching, uses thicker paper.
I would advise against home lapping, as it is better done by more experienced operators.
the best lapping is all done one direstion, from breech to muzzle.
bruce.

Bruce,
Thanks for your detailed explanation. But, as exciting as this process seems, I’m not pouring molten lead down a new/newer barrel rifle? I’ll shoot my .375s and up till the rifling wears out (never!) and then get another barrel. I’ve shot several hundred rounds through my .338 WM with no accuracy or barrel fouling issues, although I haven’t been shooting monometal bullets.
CEH

 

[CoElkHunter]

Guess I was wrong again?

mmm, you should be used to that by now.

I always thought that "lapping" had to do with auto racing.

I thought it had something to do with the outside of the barrel, then running “lapping” around a track to let the barrel cool? Silly us!

 

[bruce moulds]

c e h,
the point I was making is that you should only lap a barrel manufactured a little undersized for such purpose.
properly lapping a ready to go barrel will make it oversize, and the flame cutting of superheated powder gases doing through the gap between the bullet and groove diameter will turn jacket material into a plazma that will foul your barrel, and possibly erode the barrel significantly as well.
fire lapping does not properly lap a barrel
bruce.

 

[CoElkHunter]

c e h,
the point I was making is that you should only lap a barrel manufactured a little undersized for such purpose.
properly lapping a ready to go barrel will make it oversize, and the flame cutting of superheated powder gases doing through the gap between the bullet and groove diameter will turn jacket material into a plazma that will foul your barrel, and possibly erode the barrel significantly as well.
fire lapping does not properly lap a barrel
bruce.

Thanks for this clarification Bruce. I think I’ll just buy a pre lapped barrel/rifle if I ever decide I need one. The lapping concept is intriguing, but in a large bore rifle shooting hundreds instead of thousands of rounds over time, it just doesn’t seem it’s necessary or cost effective?
CEH

 

[Bob Nelson 35Whelen]

Thanks for this clarification Bruce. I think I’ll just buy a pre lapped barrel/rifle if I ever decide I need one. The lapping concept is intriguing, but in a large bore rifle shooting hundreds instead of thousands of rounds over time, it just doesn’t seem it’s necessary or cost effective?
CEH

@CoElkHunter
The Llijla stainless barrel for my 25 is lapped and deadly accurate.
You will find different grades of barrels from a manufacturer and most do a competition or match grade barrel that are lapped.
Yes they are a bit dearer than a,standard barrel but only yg you can decide If'n the extra money is worth it. To me they are. If you building a custom rifle why would you put a crap barrel on it.
Bob

 

[John P.]

Sometimes it is required.

This thing makes it easy. Two ball bearings in the handle.

Adapter screws on the end of the barrel to guide the rod.

A drilled out cartridge helps to center the rod.

Laps are a series of stacked leather washers with aluminum washers between. The leather holds the lapping compound. The screw on the end allows tightening of the lap.

Assembled and ready to use.

I can get the barrel warm when lapping, try to do this with a lead lap. The problem with a lead lap is it is worn out on the first stroke.

I hold the barrel in the barrel vise.