Chrome Lining Process

[Scaurus]

Hello guys and greetings from Germany!

I have a question regarding the process of chrome lining an AR barrel.

Can it be done with the barrel extension installed?

I ask, because I want to know if the gas port can also be chrome lined.
After some research I could only find gas ports that are drilled after chrome lining. I wonder whether that is done because it is just simpler and cheaper or if it's a necessity of the process.

Thanks!
Scaurus

[lysander]

For AR-type rifle barrels the chrome plating of the bore is always done after the barrel extension is installed and usually after the gas port drilled. This is done so the chamber can be finish reamed to the proper distance from the locking lugs.

However, in order to chrome plate anything you have to have an electrode and good electrolyte flow around the area to be plated. Plating inside a 0.092" hole is not worth the trouble, it wouldn't help much. The chrome plating feathers up into the port on the bore side.

[Scaurus]

Thanks for the reply, lysander! That cleared things up a lot!

I'm afraid I'm not entirely certain however what you mean by "feathering up". Do you mean there is going to be a little bit of chrome lining at the beginning of the gas port due to it being in the vicinity of the passing anode?

If that is so, is it fair to surmise that both chrome lined and nitrided barrels are equally susceptible to gas port erosion? As I currently understand it, gas ports in both kinds of these are either unlined or untreated.

Thanks again!
Scaurus

[lysander]

If you look at the muzzle or chamber end of a barrel, the chrome plating extends up the sides slightly same occurs in the gas port, but to a lesser extent.

Nitriding covers everything that is touched by the salt bath, inside, outside, gas port everything. Whether, or not, that provides increased gas port erosion, I don’t know.

Usually, gas port erosion, while it looks ugly through a borescope, does not affect barrel life to the extent of throat erosion.

[Scaurus]

Thanks lysander for clarifying the 'feathering' term, I suspected as much!
The "problem" (if one likes to obsess about such matters :)) with nitriding to my knowledge is that it should only be done without the barrel extension installed, so the gas port isn't actually drilled yet when the barrel is treated.

Before I looked into the chrome lining process, I thought that the major drawback of nitriding was the lack of protection of the gas port. Now I realize that chrome lining has the same deficiency.
For me, that means it's one less thing to worry about!

Cheers!
Scaurus

[lysander]

Gas ports are usually drilled prior to nitriding, at least I have not seem one that isn't.

It really would not be that hard to do, maybe you can "ask Faxon". The way I would do it would be to, prior to nitriding, install the extension and torque it to something less than 150 ft-lbs, say 75, then ream the chamber slightly long and drill the gas port slightly off a few degrees. Mark the two parts as a matched set and send them off to be nitrided.

When they come back torque the extension so the gas port is at 12 o'clock.

[MegademiC]

Unfortunately, the throw power of chrome plating baths is very low.

[FaxonNathan]

For AR-type rifle barrels the chrome plating of the bore is always done after the barrel extension is installed and usually after the gas port drilled. This is done so the chamber can be finish reamed to the proper distance from the locking lugs.

However, in order to chrome plate anything you have to have an electrode and good electrolyte flow around the area to be plated. Plating inside a 0.092" hole is not worth the trouble, it wouldn't help much. The chrome plating feathers up into the port on the bore side.

That is not the case. It is almost always done prior to attaching the extension. Manufactureres are able to hold fanatstic tolerances on extensions and shoulders so setting headspace is not an issue. Further, elctrolyzing a bore with a hole in it will lead to inconsistent thickness and adhesion, detrimental to accuracy.

[Junkie]

My understanding is that the thickness of chrome lining is enough that you need an oversized bore, and that it can't reasonably be done to a finished barrel for that reason.

As FaxonNathan says, chrome lining is done before attaching the extension.

[FaxonNathan]

My understanding is that the thickness of chrome lining is enough that you need an oversized bore, and that it can't reasonably be done to a finished barrel for that reason.

As FaxonNathan says, chrome lining is done before attaching the extension.

You can do it two ways - oversized bore or polish the inside the amount of material to be removed.

[lysander]

That is not the case. It is almost always done prior to attaching the extension. Manufactureres are able to hold fanatstic tolerances on extensions and shoulders so setting headspace is not an issue. Further, elctrolyzing a bore with a hole in it will lead to inconsistent thickness and adhesion, detrimental to accuracy.

Interesting, I would have though the chrome might flake around the hole.

Does this mean the threads on the extension are timed?

[MegademiC]

Interesting, I would have though the chrome might flake around the hole.

Does this mean the threads on the extension are timed?

Plating done correctly does not flake.
Flaking plating is due to failed cleaning, failed activation, or something getting on there that shouldn't somewhere in the process.

Edit, or if you dissolve what's under it, as can happen with decorative chrome.