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Teach me to lap barrels (PLEASE)!

 
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  #1  
Old 12-26-2012, 08:30 PM
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Teach me to lap barrels (PLEASE)!

OK, I'm not a dummy but I have no experience in this area so I may sound like one. Years ago I worked as a machinist to put myself through engineering school so I don't think this should be beyond me. I just need to know where to start.

Is there a good reference on barrel lapping? Do I need to create a plug to imbed the lapping compound into or can I simply use it on a patch or swab?

Any guidance is appreciated!!

Thanks!
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  #2  
Old 12-26-2012, 09:27 PM
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Location: Texas
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Re: Teach me to lap barrels (PLEASE)!

Quote:
Originally Posted by Buano View Post
OK, I'm not a dummy but I have no experience in this area so I may sound like one. Years ago I worked as a machinist to put myself through engineering school so I don't think this should be beyond me. I just need to know where to start.

Is there a good reference on barrel lapping? Do I need to create a plug to imbed the lapping compound into or can I simply use it on a patch or swab?

Any guidance is appreciated!!

Thanks!
Everyone has to start somewhere,so hear goes.

I suggest you find a factory take off and practice on it first.

To do a proper job you almost have to have a bore scope, But if you dont you can use a tight
patch as you go to feel the improvement.

Buy some fine lapping compound (1000 to 1500 grit non embedding) dont use valve grinding compound (To aggressive).

Using an old bore brush brush with some of the bristles ground off (About half way down the
brush )place the brush in the bore from the reciever end about 1'' from the muzzle.

Next ; Melt some tire weights or plumbers led and carefully pore the led down the barrel until it
fills to the top.

After cooling you can push the casting out the crown and trim the sprue off. I would recomend that you practice this step until you can cast a good pill.

When you have that mastered, apply a small amount of lapping compound to the casting and insert it back in the muzzle with the cleaning rod attached threw the action/breach. (Note do not turn the broach around, place it in the same location and orientation as it was cast. Carefully start the broach by hand in the rifling. once started place the barrel horizontal and begin to lap never allowing the casting to exit the barrel.

A word of caution: don,t over do it , lapping causes barrel wear and shortens life . so this is a case
of "Less is More" . only lap enough to smooth some of the tool marks out. the bullet will do the rest
with time.

If lapping is done incorrectly it can ruin a good barrel, so practice on an old or take off barrel first and then if you are still intent on proceeding , be careful.

J E CUSTOM
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Old 12-27-2012, 12:09 AM
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Location: Idaho Falls, Idaho
Posts: 539
Re: Teach me to lap barrels (PLEASE)!

That's one of the best, most straight forward method I've seen. Thanks for sharing.

Dan
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  #4  
Old 12-30-2012, 09:26 AM
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Posts: 798
Re: Teach me to lap barrels (PLEASE)!

Quote:
Originally Posted by J E Custom View Post
Everyone has to start somewhere,so hear goes.

I suggest you find a factory take off and practice on it first.

To do a proper job you almost have to have a bore scope, But if you dont you can use a tight
patch as you go to feel the improvement.

Buy some fine lapping compound (1000 to 1500 grit non embedding) dont use valve grinding compound (To aggressive).

Using an old bore brush brush with some of the bristles ground off (About half way down the
brush )place the brush in the bore from the reciever end about 1'' from the muzzle.

Next ; Melt some tire weights or plumbers led and carefully pore the led down the barrel until it
fills to the top.

After cooling you can push the casting out the crown and trim the sprue off. I would recomend that you practice this step until you can cast a good pill.

When you have that mastered, apply a small amount of lapping compound to the casting and insert it back in the muzzle with the cleaning rod attached threw the action/breach. (Note do not turn the broach around, place it in the same location and orientation as it was cast. Carefully start the broach by hand in the rifling. once started place the barrel horizontal and begin to lap never allowing the casting to exit the barrel.

A word of caution: don,t over do it , lapping causes barrel wear and shortens life . so this is a case
of "Less is More" . only lap enough to smooth some of the tool marks out. the bullet will do the rest
with time.

If lapping is done incorrectly it can ruin a good barrel, so practice on an old or take off barrel first and then if you are still intent on proceeding , be careful.

J E CUSTOM



Thank you! I appreciate the detail.

I presume residual oil and lack of flux will be enough to ensure the lead doesn't adhere to the barrel. I have a lead pot & plenty of lead so that part is easy.

Lapping compound comes with either silicon carbide or aluminum oxide grit. I lean towards silicon carbide as the size of the grit is more consistent. (Since it's crystalline shape makes it a little more aggressive a finer grit works as well as a coarser aluminum oxide grit.) From my understanding neither will imbed in steel although silicon carbide will imbed in aluminum so I'm not sure what you meant by "non-imbedding". Which is recommended?

This barrel is so rough it's hard to look at anything being done to it as "ruining" it. It's trash as it is & may be good once lapped. Currently it will only fire 3 shots before there is so much copper in the barrel it goes way over-pressure.

Thanks again!!

Last edited by Buano; 12-30-2012 at 09:57 AM.
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  #5  
Old 12-30-2012, 10:05 AM
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Join Date: Jan 2005
Location: OK
Posts: 2,145
Re: Teach me to lap barrels (PLEASE)!

The only thing I will add to JE comment is that you need much coarser grit than 1000.
most barrel makers lap with a specific abrasive(I don't recall which one) but it is between 120 and 150 grit. The abrasive embeds in the softer lead and this is why the process works, as the barrel is lapped this abrasive breaks down and will actually produce a finer finish but no where near what 1000 grit would polish.

I have been given this abrasive and used to lap at least a dozen barrels, a good lube added to the bore aids in the process, and mixing the abrasive with oil and applying to the lead lap also helps hold the abrasive until you pull the lap into the bore.
Within about 3-5 strokes you can feel the lap slide freer as the abrasive works into the lead and fractures to smaller grit.
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  #6  
Old 12-30-2012, 03:10 PM
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Location: Great Falls, MT
Posts: 4,716
Re: Teach me to lap barrels (PLEASE)!

Quote:
Originally Posted by Coyboy View Post
The only thing I will add to JE comment is that you need much coarser grit than 1000.
most barrel makers lap with a specific abrasive(I don't recall which one) but it is between 120 and 150 grit. The abrasive embeds in the softer lead and this is why the process works, as the barrel is lapped this abrasive breaks down and will actually produce a finer finish but no where near what 1000 grit would polish.

I have been given this abrasive and used to lap at least a dozen barrels, a good lube added to the bore aids in the process, and mixing the abrasive with oil and applying to the lead lap also helps hold the abrasive until you pull the lap into the bore.
Within about 3-5 strokes you can feel the lap slide freer as the abrasive works into the lead and fractures to smaller grit.
I'm sure the "all knowing one" will be here shortly to straighten us all out!
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  #7  
Old 12-30-2012, 05:55 PM
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Re: Teach me to lap barrels (PLEASE)!

I hear you brother!
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