Bore Lapping

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smoothshooter

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If I wanted to lap the bore of a revolver, or a rifle for that matter, what would be wrong with putting a small amount of the appropriate grit of polishing compound on a patch and making several passes up and down the bore , leaving a very light coating? Then firing a jacketed bullet at low velocity followed by a cleaning, then reapplying the polishing compound, and repeat.
it would be easier than the casting a slug on the end of a rod method.

I am afraid if the polishing was done by simply applying the compound to a tight patch, and repeatedly swabbing the bore, it would not get in the corners of the rifling good enough.

Any thoughts?
 
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A friend bought a kit .It came with lead bullets and some abrasive paste that you rolled the bullets in then reloaded with a light charge of powder .I do believe it's called fire lapping.
I'd try some JB bore paste on a patch a few times . In my opinion I would not fire a jacketed bullet with the lapping compound.
 
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I have fire lapped barrels on a few handguns and rifles that were obviously rough, and leaded excessively, or were inaccurate. More often than not, it works. But before I did, I would make sure the barrel actually needed it. Leading can be caused by a rough barrel, but can also be caused by a variety of other issues, same with accuracy. A bore scope is nice, but you can check for burrs and tight spots by slowly pushing a dry cleaning patch down a clean, dry bore. You should be able to feel tight spots, or feel it catch on burrs. Even then, accuracy may be fine, and leading may be minimal. Each gun is different. Cant really say if it will improve accuracy in a gun with an already good bore. Some bench rest shooters lead lap their barrels, some don't. Both schools of thought produce some pretty small groups. If a gun is producing acceptable accuracy with no undo leading or fouling, I would leave it be.

The last gun I did was a Lyman black powder rifle I bought last year. Beautiful on the outside, the bore looked one step above a sewer pipe. Could barely load it, and it key holed conicals at 25 yards. First, I scrubbed the bore with PB Blaster and a brush wrapped in steel wool to remove the rust and scaling. Then I fired 20 patched round balls with the patches soaked in a fine valve grinding compound, with a good cleaning after each 3 shots. When I was done, the gun was easy to load, and places 420 grain lead conicals in fist sized groups at 50 yards with iron sights. Not bad for a $75 parts gun.

Larry
 
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When I bought a .22 Ruger American Rimfire rifle for my grandson, On the advice of a member on another forum, the first thing I did was run a patch coated with JB bore paste down the barrel about 30 times from breech to muzzle. I don't know it this did any good but that gun shot MOA groups using CCI mini mags from that day forward.

I filed those results under "further research needed".
 
One thing I found when researching lapping a year ago was the statement that lapping should be done BEFORE cutting the chamber.

If true, it is probably too late to lap your barrel. Except for the fire lapping.
 
The BEST way to lap a barrel is to shoot it. Not being "cute" either - just shoot the thing and it will soon smooth out.

I have been shooting for 50 years and have yet to HAVE TO purposely lap a barrel with anything other than bullets. Unless there is a specific problem I don't understand why you would want to do this. Am I missing something?
 
chief38 said:
The BEST way to lap a barrel is to shoot it. Not being "cute" either - just shoot the thing and it will soon smooth out.

I have been shooting for 50 years and have yet to HAVE TO purposely lap a barrel with anything other than bullets. Unless there is a specific problem I don't understand why you would want to do this. Am I missing something?
Click to expand...

Yes. A lapped barrel is a more accurate barrel.
 
"Yes. A lapped barrel is a more accurate barrel."

What reference material is out there to verify this? I find this interesting as I have also been shooting a long time and the only time people suggested "after assembly lapping" of the barrel was if there's a problem.
 
moosedog said:
"Yes. A lapped barrel is a more accurate barrel."

What reference material is out there to verify this? I find this interesting as I have also been shooting a long time and the only time people suggested "after assembly lapping" of the barrel was if there's a problem.
Click to expand...

Not my job, Mon.
 
In revolvers there is sometimes a smaller diameter in the bore caused by the barrel being twisted into the frame too tightly. This is called a "crush fit" where the friction of the back of the barrel against the frame is used to hold the barrel in place. I have seen up to .002 reduction of diameter where the barrel is threaded into the frame, depending on how much crush it took to get the front sight vertical.

This causes excessive leading and poor accuracy. One solution is to power lap the bore until it is all the same size. I think the best remedy is to remove the barrel and face off the back until the front sight is only about 5 degrees to the right with hand tightening. When the barrel is removed it springs back to the original diameter. It can then be refitted, with Loctite if needed, and the restriction just ahead of the forcing cone will be gone.
 
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The Fire Lapping process has be around for a long time and has been discussed ad nausiem in the gun rags and all over the internet. If your not much of a do it your selfer, their are kits available from Beartooth Bullets.
Over the years I've firelapped rifles, pistols and revolvers. In my experience, when done right, it will do no harm to your gun. In some guns, it will slightly improve accuracy. (mostly with lead, coated or plated bullets) In every gun I've lapped, it reduces bullet fouling buildup.
What it will not do is turn a 5 MOA gun into a 1 MOA gun. It's not magic.

Jeff
 
I don't know how much if any improvement in accuracy there is after barrel lapping, however I do know that pretty much every guns barrel produced over the last 60 years or so is probably capable of shooting more accurate than we are. While there are many defects in modern S&W shipments as long as a barrel is not actually defective, they seem pretty darn accurate (consistent) from every one I've actually shot.

Unless someone is literally an Olympic competitor, barrel lapping is about the last thing I would be concerned about in upgrading a Smith Revolver. If a barrel on a new Smith is bad enough to adversely affect accuracy, I'd definitely recommend sending it back to the Factory.

If I was competing in the Olympics, even then while barrel lapping might be a reasonable option I would think that increasing the Competitors mental advantage from the lapping would be more important than that of the actual lapping itself.

I could be wrong - since I have only been shooting for 50 years (and up 'till recent times was a competitor). ;)
 
Fire lapping my 2 inch Mod 63 seems to have significantly improved accuracy. I did the lapping to reduce the barrel constriction under the frame threads. 25 yd groups went from about 5 inches to about 3 1/2 inches.
 
LBT has the fire lap kits and detailed instructions. It includes enough compound to lap every gun you'll ever own.

The primary purposes of lapping is to clean up a rough bore and/or get better accuracy from cast bullets. If your gun already shoots well with cast of your planning to shoot jacketed, fire lapping is a tedious exercise for little or no gain.


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