Lapping A Barrel

[birdiemc]

Seeing all these pictures folks are posting with their new borescopes got me interested in learning more about lapping a barrel. It seems that hand lapping needs to occur before crowning and cutting the chamber, so doing it to a factory barrel is not an option. There are the lapping bullets, which I know have strong supporters and strong opponents. I found this below and it seems he's putting some abrasive on a patch to try and smooth out some of the irregularities so what are opinions on this approach?
https://www.google.com/url?sa=t&sou...Vaw1fyjfgb294Z80fmcZ5UBJZ&cshid=1577152095667

 

[birdiemc]

I'm also interested in hearing from some folks who have lots of experience correctly hand lapping a barrel, do you have any before and after pictures to show what difference it makes.

 

[KyCarl]

A correctly lapped barrel is checked in the .0001's Bore gauges of the length and quality needed ain't coming from Harbor Freight. Something better left to someone who has the experience and equipment. A gob of lapping compound on a patch will not stay concentric or parallel You will just wallow out a low spot...

 

[birdiemc]

A correctly lapped barrel is checked in the .0001's Bore gauges of the length and quality needed ain't coming from Harbor Freight. Something better left to someone who has the experience and equipment. A gob of lapping compound on a patch will not stay concentric or parallel You will just wallow out a low spot...

Well the abrasive on a patch idea seems pretty bad because it's going to round off the corners of the lands vs. keeping them nice and sharp, so I'm not suggesting that it's something I was going to try...I'm just curious about the before and after of a correctly lapped barrel.
A job I once held I used to have to lap flat brass seals, our surface plate was Grade AA, so if I recall correctly that's flat to .000001" and is what was required to get two pieces of brass to create a liquid tight seal, so I understand the level of precision equipment that's required to do that.
I just want to understand better how that all works in the barrel of a rifle.

It's interesting that you say they measure with a bore gauge accurate to .0001. Any picture I've seen from somebody slugging their barrel the slugs usually have voids and strange markings. It seems the slugs would also pick up any tool Mark's left behind which wouldn't seem ideal as they would create a high or low on the lap maybe? Also does the molten lead poured into the muzzle cause it to expand in that area resulting in a lap that is larger than desired? All just things I'm curious about. I posted in the gunsmithing forum because I'm wanting to hear from people with true knowledge on the subject not just what they read in a magazine or on the internet somewhere. But I dont know...do gunsmiths lap barrels or just only use factory lapped barrels?

 

[Barrelnut]

I use JBs for cleaning from time to time; usually when I want to get all the copper out, etc. to go do a different bullet or put the rifle away for the year. I don't think JBs would actually lap a barrel. It certainly wouldn't remove any tool marks. It's just not that aggressive. If you use the JB's to get down to metal and clean out all of the fouling, I believe the JBs red would probably polish things a bit.
I would certainly try this method though before trying something like fire lapping. Fire lapping can actually erode the lands a bit. I ruined a barrel one time with fire lapping...

 

[J E Custom]

I have done many factory barrels and the correct way is to do a minimum lap using a lead lap cast in the bore near the muzzle several inches long so it will follow the rifling accurately. I like to use a non embedding compound with 1200 to 1500 grit so it just takes the high spots off and doesn't reduce the diameter any measurable amount. Valve grinding compounds and other 400 to 800 grits are to aggressive and will do more damage than good. I tighten the lap so it wont turn on the rod so I can start it in the groves in front of the freebore of the chamber and push it all the way through without stopping. I also recommend using a bore guide to start the lap straight in an effort to save the lead angle and the first 1/2 " on the bore. (If you saw it back and forth It will bell out the muzzle and the breach end of the barrel, hurting accuracy).

After the first lap is used and begins to wear, I like to cast a new one and put the finishing touch on the bore following the same procedure. When you buy a custom hand lapped barrel, This belling is cut from the muzzle and the reamer takes care of it on the chamber end. I prefer not to do factory barrels because it will take away from barrel life and if not done sparingly, hurt accuracy. Lapping a factory is a last ditch effort to capture some reasonable accuracy.

This is just what works for me

J E CUSTOM

 

[Hespco]

I've done a fair amount of lapping using 1200 grit & finishing with Jeweler's Rouge. I cast bullets from pure lead & then roll them lightly in the abrasive. Using just enough powder to push them completely thru the barrel. Usually 7 or 8 rounds of 1200 ( very fine ) grit, then clean the bore. Another 10 with Jeweler's Rouge does it . This smooths out any small scratches or burrs. Has worked successively for me with several rifles over the years.

 

[Mram10us]

I was thinking on this last night, but was wondering if anyone had used epoxy rather than lead??? You'd think marinetex or devcon would be strong enough to polish up a bore ....

 

[birdiemc]

I was thinking on this last night, but was wondering if anyone had used epoxy rather than lead??? You'd think marinetex or devcon would be strong enough to polish up a bore ....

What's your reasoning for wanting epoxy instead of lead? Just thinking out loud here but I think it might provide fewer voids than I've seen on the lead slug pictures people have posted. Definitely harder than lead but dont know if that would be an advantage or not.

 

[J E Custom]

I would not recommend trying anything but lead because when lead cools It also shrinks enough to remove it You might end up with a permanent plug in the barrel.

With lead, the small amount of shrinkage allows room for the abrasive and allows it to embed in the lap for consistent application.

I once tried Cerrosafe because it only took a hot water to melt it, but there was no shrinkage (Which is what it is supposed to do) And the lap could not be inserted with the compound on it because it was to tight.

Plumbers lead seems to be the best material to do an accurate cast with. Some times the cast doesn't turn out to good because the barrel cools it to quick. So use a heat gun or hair drier to warm the barrel for better results. I use old bore brushes and grind most of the brisle's off the brush and leave a few on the back of the brush to catch the lead and hold it firmly on the brush. it then attaches to the cleaning rod for use.

By the way, I still don't recommend this process for someone that has never done it but if you are dead set on doing it for the first time I would try it on an old take of barrel just to be safe.

J E CUSTOM

 

[Mram10us]

What's your reasoning for wanting epoxy instead of lead? Just thinking out loud here but I think it might provide fewer voids than I've seen on the lead slug pictures people have posted. Definitely harder than lead but dont know if that would be an advantage or not.

Epoxy is just easier to apply. No heating up and if you spill it, it won't damage things. Plus, my lead pot is full of salts for annealing.

 

[Mram10us]

I would not recommend trying anything but lead because when lead cools It also shrinks enough to remove it You might end up with a permanent plug in the barrel.

With lead, the small amount of shrinkage allows room for the abrasive and allows it to embed in the lap for consistent application.

I once tried Cerrosafe because it only took a hot water to melt it, but there was no shrinkage (Which is what it is supposed to do) And the lap could not be inserted with the compound on it because it was to tight.

Plumbers lead seems to be the best material to do an accurate case with. Some times the cast doesn't turn out to good because the barrel cools it to quick. So use a heat gun or hair drier to warm the barrel for better results. I use old bore brushes and grind most of the brisle's off the brush and leave a few on the back of the brush to catch the lead and hold it firmly on the brush. it then attaches to the cleaning rod for use.

By the way, I still don't recommend this process for someone that has never done it but if you are dead set on doing it for the first time I would try it on an old take of barrel just to be safe.

J E CUSTOM

I have some old barrels and a borescope. I'll give her a try and let you know how it goes. A patch of trans fluid for a release agent should work or maybe some paste wax. Thoughts?

 

[birdiemc]

I've always had good luck with kiwi or paste wax as a release agent. Never tried trans fluid but that stuff does everything so why not...

 

[MNbogboy]

Agreeing with JE, the lead lap shrinks just enough for easy removal/movement. Even with too much of abrasive the lead is hard to move. I would think the epoxy would be too tight. Also having only tried this on a couple of "rough" factory barrels (7 or 8 laps cast) everyone broke loose easily. Another advantage of the lead would be no "drying/curing" time. The lead lap will be ready before you can shut off the torch. Also you don't need a led pot as a small ladle/dipper will hold way more than you need per pour and you can melt it with a propane torch.
My guess if the epoxy fits like bedding an action it could easily mechanical lock because of the rifling twist & "rough" button bores.
Not saying it wont work, especially with the right epoxy. Try it on a couple of tomatoe stakes and let us know.
My .02,
Randy