Superior Barrel Lapping Method

FMP Airsoft said:

Ah yes, let me just get out the lathe I have lying around.

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SiliconeSword said:

I can machine the black piece of an AA chamber into the barrel but it's not ideal as AA has pretty bad tolerances over the years.

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SiliconeSword said:

This is an edited version of this guide, to make lapping easier for noobs.

Description
To start off, lapping is a type of polishing where you only remove high spots from a surface, while polishing will remove material from all surfaces. Polishing will shine a surface, but lapping will flatten a surface, which can then be polished. It's often used for precision machinery and tools, such as some hydraulic and pneumatic cylinders.

This is important in airsoft as many guns come with a barrel that has a visibly rough bore, which will cause turbulent air, or even cause impacts on your BBs which will make your accuracy mediocre to terrible. This is one of the significant differences between an upgrade barrel and a bad stock barrel, with bore diameter and material being the other two.
Material doesn't matter much unless your barrel is aluminum, and bore diameter doesn't have a significant impact on accuracy, so with a little bit of work you can have your own high end barrel without spending much money.

Stuff
The starting place in this is a lap, which is a round rod of some sort, of a similar diameter to your barrel. There are 3D printed laps for sale, but I've found that a simple wooden rod is superior, and far cheaper as well. I was lucky enough to find some 6mm bamboo rods, but if you can't find something that size, you will need to get a 1/4 inch wooden rod and sand it down to the correct size. For size, you want a rod a few inches longer than your barrel, and for diameter you want the rod to be a slip fit in the barrel. You don't want the rod to be tight, and you don't want it to be wobbly, you want it to glide with a little bit of pressure.
If you are starting with a larger rod, I recommend putting some pencil dust inside your barrel, and then insert your rod and look for dark spots. If there is a dark spot that gives resistance, just sand or scrape it off and continue along the whole rod.

The next part is the cutting/polishing compound, which there are two main paths for.
If you have a steel barrel you will absolutely want diamond lapping compound as steel is very abrasion resistant, but if your barrel is brass, you can get away with normal liquid metal polish you would find at an auto parts store.
And an optional thing is some sort of device like a drill or lathe, that you can put your barrel into to speed the process up.

Starting
Stage 1
You will start by inspecting the inside of your barrel, and decide how rough the barrel is.
Usually a good starting place is 20-30 micron compound, that you will spread along the rod.
You will then insert the rod, and slide it from one end of the barrel to the other, keeping it centered and not putting too much pressure on one part of the barrel. You will simply repeat this, with an occasional twist, until the bore looks good. To check the bore, refer to my barrel cleaning guide in my signature.
Also, this is a stage where you can use a drill or lathe to spin your barrel, and you can do this up to the 10 micron point.
You will likely start to gain more backspin with the same hop setting due to there being less friction between your BB and barrel, which may be a bother in some guns, but there are many workarounds.
Stage 2
Once your barrel looks good, you can stop there, or keep going.
To keep going, move onto 10-15 micron compound, and repeat this stage.
You can spin your barrel if you have a tool to do that, but if you choose to do that it is good to then just do push lapping afterwards, as this provides a better finish.
Stage 3
Once your barrel looks good, you can stop there, or keep going.
To keep going, move onto the next size, probably 3-7 micron.
Going finer than 10 micron may not be great if you have an HPA engine or a GBBR as this will make your barrel more slippery and you may notice inconsistent hop due to the BBs being "kicked" deeper or shallower into the barrel. If you notice this, you can try and make your gun not do that, or you can use a coarser compound on the first couple inches of barrel.
For AEGs this will likely not be an issue, but may manifest in some cases.
For snipers, I don't think this is an issue.
Finer than 10 micron doesn't do much for accuracy I've noticed, but it's worth a try.

Tips

• Start lapping from the muzzle end of your barrel, and only lap a little bit on your hop end in order to get the bottom below the window smooth
• Clean your barrel thoroughly between compound sizes to avoid scratches
• Use separate rods for separate compounds
• Use spin lapping for 10-40 micron, it is faster and is good for a really bad barrel
• Use diamond for stainless or plated barrels
• Rotate your lap about 1/10 turn every now and again to wear the barrel evenly
• Guns with a violent loading mechanism like HPA engines, some GBBs, and maybe a few select AEGs may seat BBs inconsistently for depth, leading to inconsistent hop.
• If you can't get consistent hop from your gun after trying a number of things, go back a stage in compound
• A well lapped barrel will appear black and reflect no light if looked at from certain angles.
• Watch a movie while doing this, I highly recommend Countryman, available for free on youtube

Don't be intimidated by this, it is rather easy to do, and will provide very good results in most cases.

HERE IS A PLAYLIST OF GOOD LAPPING INFO
HERE IS SOME DECENT DIAMOND COMPOUND

Here is a cross section of a piece of one of the fat barrels I make lapped to only 14 micron
View attachment 19007

From left to right
ZCI, Angel Custom, PDI(factory 20 micron), EdGi(factory 7 micron)

View attachment 19008

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