Teach me to lap barrels (PLEASE)!

Buano

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Nov 28, 2009
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902
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!
 

J E Custom

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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
 

Buano

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Joined
Nov 28, 2009
Messages
902
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:

Coyboy

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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.
 

FEENIX

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Great Falls, MT
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! :rolleyes::D:cool:
 

BountyHunter

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IMO you are going to make a lot of barrel mftrs real happy!

There is a reason the mftrs cut off the last 3/4 to 1" of the barrel when done lapping. The guys that do it for a living all day cannot keep from opening up the end of the barrel and you really think you can?

You have no idea what you are doing. No idea of what the initial and final dimensions will be and no way to measure anything. Plus you asking for advice from people that do not do it for a living. Call krieger or Tim North at Broughtkn and see what they tell you.

Think about that for a moment. Recipe for disaster on a barrel.

Yep they will be real happy with you screwing up the barrels!
 

Coyboy

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BH I agree, OP if your working with something you don't mind destroying go ahead.
A bore scope sure would help you determine what you are accomplishing as well.
If the barrel is already chambered you risk washing out the throat, the barrel crown can always be cut back and re crowned.

I practiced on a couple of remy take offs, then tried it on a adams and bennit barrel that still needed to be cut down and chambered.
 

Damascus

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Why not try that "Tubbs Final Finish" system (may not be the proper product name...) , where you fire a few bullets that are coated with a mild abrasive, starting with coarse and ending with fine... I havent used it, but Ive handloaded the abrasive bullets for a few of my customers, and a couple have gotten good results.. especially with old mil-surp rifles. Personally, I would invest in a borescope before attempting hand lapping. Good luck!
 

SidecarFlip

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A Hawkeye will set you back about 800 bucks btw. I have one and it's great to use for checking your cleaning regimen. I use mine in the shop for looking in machined cavities, checking internal threads and looking inside assemblies that can't be taken apart.

Great tool. I got one for the guns and I've used it for everything else but guns.

Me. I wouldn't even consider lapping any barrel until I had a peek inside to ascertain, if, its actually a machine roughness or something else. The Hawkeye is great for checking throat erosion too.

There are some others on the market but the Hawkeye has the smallest diameter barrel. I believe it will fit a 22 caliber (223 bore).

Keep in mind, it's a precision instrument so it needs to be handled like a precision instrument but then, if you pay 800 bucks for one, I imagine you'll treat it carefully.
 

Buano

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Back when I was an aerospace engineer I had access to borescopes. When I worked at Amsco Scientific we worked with them regularly. Sure I would like to have one now, but I can't hardly justify the cost of a borescope to work on ONE used rifle.

The rifle has a stainless barrel and has been fired VERY little. When I got it the first 2 shots fired OK, then I had over pressure signs with factory ammunition. After stripping all copper from the barrel I was able to get 3 shots off without any over-pressure signs, but #4 was definitely over-pressure. Stripping the copper from the barrel again got me 3 shots before the pressure spiked. With a tight patch I could definitely feel the roughness in the center of the barrel, starting about 4" from the chamber and ending about 6" from the muzzle.

I was investigating fire-lapping the barrel but it was explained to me that this was not as good as hand-laping. Looking through reviews of fire-lapping bullets I saw good results with barrels that didn't need a lot of work but less improvement in barrels that needed a lot of work. This barrel obviously needs a lot of work so I was looking at hand-lapping.

I presumed I would not lap the last inch or two of the barrel so I could avoid possible damage to the muzzle. I also have no intention of going crazy lapping the barrel — I want to do just enough that bullets, or possibly fire-lapping, could do the rest.

I also intend to replace this barrel with a longer one at some point in the future although I didn't plan on doing that immediately. I accept I bought a gun that was "less" than I expected and, under the circumstances, I paid too much. I got burnt — the question now is how to mitigate the damage. Do I fire-lap it? hand-lap it? or simply order a new barrel? (There is one other option, ship it to the factory & tell them to figure out why this happened.)

I also looked into having the bore electro-polished but saw where rough barrels are generally lapped prior to electro-polishing. I presume this barrel would need to be lapped prior to electro-polishing.

My post here was to understand hand-lapping barrels so I could decide if this was the way to go. I still lean towards hand-lapping, but people have given me pause to think about whether this is the right choice. The more people have said, the less I am sure this is the right way to go.
 

shortgrass

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A Hawkeye will set you back about 800 bucks btw. I have one and it's great to use for checking your cleaning regimen. I use mine in the shop for looking in machined cavities, checking internal threads and looking inside assemblies that can't be taken apart.

Great tool. I got one for the guns and I've used it for everything else but guns.

Me. I wouldn't even consider lapping any barrel until I had a peek inside to ascertain, if, its actually a machine roughness or something else. The Hawkeye is great for checking throat erosion too.

There are some others on the market but the Hawkeye has the smallest diameter barrel. I believe it will fit a 22 caliber (223 bore).

Keep in mind, it's a precision instrument so it needs to be handled like a precision instrument but then, if you pay 800 bucks for one, I imagine you'll treat it carefully.
+1, here! Ya' gotta' be able to see the problem/see what you're doin'. Other wise is just a darned poor guess. At least with a bore scope it'd be an 'educated' guess.
 

toddc

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Id fire lap it. I wouldnt run those thu a hart or lilja but a factory heck yea. Ive used it on quite a few 30 cals and had it work. Use a light load and start with the 3rd stage and run them. If that doesnt fix it hit it with a full course. What do you have to lose? Especially if you can FEEL the issue it needs some serious work.
 

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