Chromed lined barrel questions

[Peakbagger46]

A friend ordered an AR upper with a FN chrome lined barrel. Anything special about what solvents to use/avoid with chrome lining? Is a strong copper solvent like Burch’s Bore Shine safe if used correctly?

Here’s the upper in question:
https://palmettostatearmory.com/psa...-lok-upper-w-mbus-sight-set-no-bcg-or-ch.html

 

[35 Whelen]

I think chrome is pretty much impervious to any and everything, that's the idea behind lining barrels with it.

35W

 

[taliv]

Chrome is not particularly sensitive to any cleaning products I’m aware of. Protect the crown from your cleaning rod, but otherwise you’re not going to hurt the bore.

 

[DustyGmt]

Stay away from hydrochloric and muriatic acid and he will be all set, lol.

 

[JDGray]

I think chrome is pretty much impervious to any and everything, that's the idea behind lining barrels with it.

35W

I think it was for wear, in full auto applications.

 

[Project355]

Impervious to rust in SE Asia, wheras chrome lined bolt carriers, forward assist, etc were also implemented after a short time of service. You can look up M16 vs M16A1 differences and get all the backstory.

All about durability and keeping the rifle in service.

 

[Speedo66]

Chrome bore holds up well to bi-metal jackets from cheap Russian steel ammo in SKS’s. Probably the same for mildly corrosive ammo.

 

[35 Whelen]

I think it was for wear, in full auto applications.

I believe you're exactly right!

35W

 

[Hjalkarsson]

from what I read, the chamber was chromed first then shortly afterward they started chrome lining the barrel too. may not be the first example of chrome lining, there are plenty of other military rifles that have chrome lining. early chrome lining had problems with peeling or chunks coming off in the barrel.

whatever their reasoning was, the effects were that the chrome lined chamber and barrel prevented rust in the jungle climate of southest Asia, made it easier and faster to clean, and greatly slowed throat erosion.

that last one is probably the most important because throat erosion has more of an effect than worn out rifling. you are much more likely to shoot out a barrel due to throat erosion before the rifling is worn out. it works because, given the usage, most throat erosion would occur during periods of rapid fire and high temp. hard chrome withstands heat much better than bare steel.

as for the cleaning chemicals, I don't think there is anything that can hurt chrome that would be even worse for bare steel. anything normally used to clean a normal rifle can't be bad for a chrome lined barrel.

the FN CHF barrels are chrome lined almost twice the thickness of regular chrome linings. while the thickness of chrome lining used to have some variation leading to loss of accuracy, the process has been refined over the years and it got more accurate, allowing FN to get away with such a thick lining.

the metal is the same proprietary blend of steel that they use for their heavy duty machine gun barrels. not like it's some sort of Wonder Metal, there are many examples of far tougher metals, but those would be impossibly difficult to machine into a barrel and would cost several times as much. this is the toughest practical metal to make a gun barrel out of. however the CHF process, while toughening the metal and speeding up manufacturing, is not conducive to accuracy and they are only required to have 4 MOA. not saying the end product will shoot that bad but these are purpose built for military applications not target shooting.

 

[Peakbagger46]

from what I read, the chamber was chromed first then shortly afterward they started chrome lining the barrel too. may not be the first example of chrome lining, there are plenty of other military rifles that have chrome lining. early chrome lining had problems with peeling or chunks coming off in the barrel.

whatever their reasoning was, the effects were that the chrome lined chamber and barrel prevented rust in the jungle climate of southest Asia, made it easier and faster to clean, and greatly slowed throat erosion.

that last one is probably the most important because throat erosion has more of an effect than worn out rifling. you are much more likely to shoot out a barrel due to throat erosion before the rifling is worn out. it works because, given the usage, most throat erosion would occur during periods of rapid fire and high temp. hard chrome withstands heat much better than bare steel.

as for the cleaning chemicals, I don't think there is anything that can hurt chrome that would be even worse for bare steel. anything normally used to clean a normal rifle can't be bad for a chrome lined barrel.

the FN CHF barrels are chrome lined almost twice the thickness of regular chrome linings. while the thickness of chrome lining used to have some variation leading to loss of accuracy, the process has been refined over the years and it got more accurate, allowing FN to get away with such a thick lining.

the metal is the same proprietary blend of steel that they use for their heavy duty machine gun barrels. not like it's some sort of Wonder Metal, there are many examples of far tougher metals, but those would be impossibly difficult to machine into a barrel and would cost several times as much. this is the toughest practical metal to make a gun barrel out of. however the CHF process, while toughening the metal and speeding up manufacturing, is not conducive to accuracy and they are only required to have 4 MOA. not saying the end product will shoot that bad but these are purpose built for military applications not target shooting.

Thank you, that was very helpful!