What is the Diff. between a "chrome moly" and a regular "Chrome Lined"??

I have always thought there was just non-hrome lines and chrome-lined....now look what I have to deal with!

Chrome-moly is a type of steel, such as "Chrome-moly 4140", a typical gun barrel steel.  This is steel which has chromium and molybdenum.  

In addition, mil-spec barrels, since the M16A1 during the Vietnam War, have their bores and chambers chrome plated, or "chrome lined".  Only the bore and chamber, not the outside.  This is for resistance to corrosion in humid jungle environments.  And while it does make cleaning the bore and chamber easier, according to at least a few manufacturers, it detracts from accuracy.  (This is highly debate on this board.)

Then there are stainless steel barrels.  Usual material is 416F stainless.  This steel is excellent for barrels, and according to my machinist friends, is more similar to chrome-moly than it is to a true stainless steel.  This material, naturally, would not require chrome lining of the bore and chamber, as the material itself is resistant to corrosion.  This is a favorite material for match barrel makers.  Some shooters do not want a shiny barrel reflecting light.  Stainless barrels can be had with black oxide coatings, or can be black tefloned.  

It is said that stainless is not good for sustained high rates of fire, as it retains heat more than chrome-moly.  I have three rifles with 416F stainless.  The heat issue is a non-issue, at least to me, firing only semi-auto.  Perhaps for a full-auto military or LEO rifle that may be a different story.

I have both stainless and chrome-moly barrels in my assortment of rifles, but wish they were all stainless.  If I lived in a drier climate, chrome-moly would be just fine, I am sure.  I personally would not pay a premium for a chrome-lined barrel.  That is my opinion, others on this board will give you differing advise.  

(Edited to correct spelling of "molybdenum".  Duh.)

Thanks for the post,
I am just more concerned about which one is better for a combat scenario. I guess that would be the "Chrome-Lined". Why isn't the Chrome-Moly barrels in Military Spec?

If you are a regular AR guy - not an ultra-top match shooter, etc. - but are like many of us here, owning one for defense, plinking, general target shooting, etc. GET A CHROME-LINED BARREL.

"Chrome-lined" means chrome lined chamber and barrel. The barrel itself is likely chromoly steel. Milspec barrel steel is 4150, used by Colt, Bushmaster (and I think Armalite). Other vendors tend to use 4140 which is a bit cheaper; I don't know the real details why 4150 is better than 4140...

Many smaller vendors tout 'chrome moly' or 'chromoly' barrels like they're something special - they're not; they're the typical steel out of which you'd make a rifle barrel. But since there's the 'chrome' involved they're trying to keep up with the 'chrome lined' folks on the features list; I think it's a bit dishonest.

Chrome lined barrels wear far more slowly than unlined barrels due to higher 'lubricity' (easier bullet traversal). They resist heat better and have far less chamber erosion than their unlined brethren. (Typically, barrels wear out in the front of the chamber area before the rest of the barrel bore wears out. Some barrels on other rifles - like the STG58 FAL - had only a chrome-lined chamber but not bore.) Chromed bbls are far more easily cleaned than non-chrome-lined barrels, and have fewer chambering problems (smooth chamber, no roughness, etc. - common prob in bottom feeder ARs). They really don't need a break-in period or special treatment - just start shooting, and clean when appropriate.

Don't use Hoppe's #9 on a chrome-lined barrel unless you clean it well immediately afterwards
as it can hurt the chrome lining. BreakFree/CLP is all you need (Tetra prob a decent substitute.)  

Also, you cannot 'touch up ream' a chrome-lined chamber unlike an unlined one - once it's made, it's that way forever. This is why chrome lining costs quite a bit extra: caustic chemicals, toxics, plus a mfg process that ends up causing rejection of a decent fraction of barrels. (I hear anywhere from 10%-20% bbls that were fine going in the process don't make it. These barrels are useless.)

Now, most chrome-lined barrels are milspec and have milspec chamber dimensions. These are a tad looser than some of the "match" chambers out there and these chrome-lined barrels will have fewer problems due to smooth chambering and looser fit. If you hang around here long enough, you'll see lotsa folks have problems using bulk/surplus ammo in "match" AR barrels with tight chambers. You want your AR to eat any kind of ammo you can get your hands on.

The statement that chrome-lined barrels are less accurate than unlined barrels has to be taken with a few grains of salt. Some of this accuracy difference may be attributable to the looser chamber a milspec chrome-lined barrel has when compared to a tight match chamber. I suspect that the best unlined barrels are maybe a tad more accurate than chromed. But everyone with cheap unlined barrels touts this as a feature when they're really no better (and perhaps worse) than a quality milspec barrel.  And the chrome-lined bbl will stay consistent far longer than the unlined bbl will. Unless you are a GREAT shooter using GREAT quality ammo (Fed Gold Medal Match or Black Hills, etc)
you won't notice the difference.

There are plenty of folks shooting Nat'l Match competitions with chrome-lined barrels and they do fine.

Save yourself grief: your first AR barrel should be chrome-lined with milspec chamber so that your intro to ARs is as trouble-free as possible. That's not to say nonchromed ARs don't work - many work fine! - but when I hear of chambering or extraction problems, 90% of the time it's somebody shooting standard ammo out of an AR with an unlined barrel or a 'match' barrel.

Bill Wiese
San Jose, CA

The mil-spec barrels are chrome moly steel barrels that happen to have their bore and chamber surfaces plated with industrial hard chrome for reasons of longevity, corrosion resistance, and the tendency to stay cleaner longer.

The same chrome moly steel barrel that is not industrial hard chrome plated (bore and chamber) would be known as a 'plain' or 'non-chrome' barrel, even though it is made of CHROME moly steel. Confusing, isn't it? Basically, you just have to remember that chrome bores and chambers are something added to the chrome moly steel barrel by the industrial hard chrome process.
When inspecting a bore, don't look for a bright reflective surface in a chrome bore! If it is, it's probably just a real clean non-chromed bore. Industrial hard chrome plating has a 'frosted' finish, unlike decorative chrome plate which is the shiny one! Confusing, isn't it?

Most barrel manufacturers contend that the chrome bore barrel is not as accurate as the non-chromed version because it is difficult, if not impossible to deposit the layer of chrome in the bore as uniformly as a well finisned, but non-chromed barrel.

I was shooting before stainless steel was used in firearms! Two reasons come to mind. One was that the steel itself was much more expensive to buy. The other is that the alloys of stainless available then were difficult to machine, causing more production time, and tooling to wear at a much faster rate. We now have alloys like 416 that cost more to purchase, but the other faults are out of the window.

Also, might I suggest for your first rifle, you get a 1x9 twist, as that will be accurate with 99% of the ammo most of us would ever want to shoot.

Also, I suggest you get one of the heavy barrels, that is, one that is not cut thin under the handguard.  Some are called heavy match (these are not the ones that are bull barrel match barrels).  The military barrels are cut to a small diameter under the handguard (A2 contour, M4 contour).  They will not be as accurate as the heavier HBAR style.

True Match bull barrels are usually .935" (or thereabouts) the full length.  These are not what you want for a general purpose rifle.  The "heavy match" barrels are in the neighborhood of .860" under the handguards.  These are the ones you want.

Look at catalogs from DPMS, Oly, J&T, to see what I mean here.

Quoted: Also, might I suggest for your first rifle

Thanks for the help, but I was just asking about the coatings of chrome inside barrels. This isnt about getting ny first AR or the likes, I have a few AR's already. But I do appreciate your insight!

Sorry, DUH!  This is what happens when I have too many windows open, reading multiple threads.

No problem free man,
I think I have come to the point where its all chrome lined for me from now on though.

Quoted: And while it does make cleaning the bore and chamber easier, according to at least a few manufacturers, it detracts from accuracy.  (This is highly debate on this board.)

If you know someone who shoot national match, they will inveriably have a stainless steel barrel, as it makes a moe accurate barrel.

The serious shooter who is into accuracy, SS is the way to go.

If you are like 95% of the shooter, whether you get chrome lined or not, it will have little effect.  Most people baby their gun, etc.

You will gain ~20-50% on barrel life, depending on how/what you shoot, by gettign a chrome lined barrel.