Home Forums Hunting & Shooting AR and Tactical Rifles Importance of Chrome-Lined Barrel and Chamber?

What are your opinions on the importance of this? Barrel life? Reliability? In ARs I'm looking at it accounts for about a $200 difference in price over non-chromed.

Thanks in advance,
Expat

Chrome lined barrels will help if you are person who like to run the AR until it is hot to touch. I built my LH AR's for hunting and used custom SS Barrel for accuracy , but built the right hand one with a Daniel Defense Chrome Lined barrel and it surprised me that it shoot my handloads under a inch at one yards , you don't give up as much accuracy as i was thinking you would with the barrel chromed lined. The best thing about chrome lined barrels, they will last longer and clean up easy.

Chrome lined bore and chamber for guns that will be general purpose guns and SS for accuracy minded guns.

Not that chrome lined guns can't be accurate but they serve more of a utilitarian role. You just won't have to worry about your barrel.

I'm guessing the nitriding a bore will prove to be superior to chrome. FN supposedly chrome lines their hammer forged bolt gun barrels and they will shoot ragged holes at 100yd.

I've heard that also. I'd have a hard time not loving a chrome lined barrel on a bolt gun if it shot well. A fast twist 5.56 would be a great place to start IMO.

what I am wondering is if a Nitrited chamber/bore will stand up to corrosive ammo as well as a chromed bore/chamber. I am thinking it will not.

Full chrome-lined bore and chamber in 7.62x39 was intended to permit delayed cleaning in combat areas when using the issued corrosive Type PS ball, but you still need to clean the rifle fairly soon in humid conditions.

I am thinking Nitrited bores would not hold up to that. On the Chrome bore with corrosive ammunition and cleaning it where does that info come from?

If you do a search on the forums I printed an email from the armor for the Army Rifle team about Melonite. He did extensive testing using machine rests and with the rifle teams. He did this over a great period of time. He was sold on melonite for both reduced barrel wear and corrosion resistance. I am leaving for Christmas right now, but will find it and post it tomorrow.

This is the email that was sent to me.




I was the Armorer for the Army Reserve Shooting Team for over a decade so I do have quite a bit of experience with both processes.

As I am sure you know, most G.I. barrels are made from chrome molly steel which is more susceptible to corrosion than stainless steel. Chrome lining is used on G.I. bores both to extend their shooting life and to protect them from corrosion that can be a problem in battlefield conditions where maintenance is sometimes sporadic or insufficient. Chrome lining does a pretty good job of protecting battlefield weapons. One of the objections to chrome lining is that it is thought to decrease accuracy. This seems to be a valid criticism and is backed up by machine rest tests I have conducted of identical barrels (same manufacturer but half chrome lined and half not).

As you are aware most barrel "wear" is in the throat area. So eventually the hot gasses from the burning of the gunpowder will eat thru the chrome lining at the throat. It is rumored that at this point accuracy will plummet but I have not found that to be true. (Or if true, it is overstated or maybe only occurs for that short period when there is both chrome and bare steel in the throat simultaneously - just at the point of initial break thru.) Chrome lined barrels can continue to shoot well for thousands of rounds after the bare barrel steel at the back of the barrel (throat) has been exposed due to erosion of the chrome lining. Another criticism of chrome lining is that it can flake off later in the life of the barrel resulting in poor accuracy. Obviously, this could also cause maintenance problems if the user is depending on the chrome to ward off corrosion and thus is careless in his bore cleaning. If corrosion is allowed to occur pitting will result and that will ruin accuracy for sure.

Barrel pitting was one of the reasons I got involved in Salt Bath Nitriding. I was loosing nearly as many expensive match grade barrels to improper maintenance (causing pitting) as I was to wear out. This was under the relatively benign target shooting conditions. Obviously given the reputation of degraded accuracy, using chrome lining wasn't an option. So for the past couple of years I have been Salt Bath Nitriding all of my match barrels and haven't had a single one exhibit any pitting. During that 2 yr. period shooters have put anywhere from a few hundred rounds to thousands of rounds on said barrels. I don't know how long the coating will persist so at this point I am still evaluating it as a preservative. I don't know what will happen in another year or two when these barrels get more wear on them. Salt Bath Nitriding goes on both inside of the bore and on the outside surface. So, instead of 2 manufacturing steps you have combined them into one. Salt Bath Nitriding doesn't degrade accuracy one iota, unlike chrome lining. This was the first thing that I verified when I began using the process. I broke in a bunch of barrels and then machine rest tested them for group. I recorded and kept the targets, cleaned up the barrels, and sent them to MMi TruTec for the Isonite process. When they came back I reassembled them on the same receivers with the same torque settings, same bolt carrier assemblies, same flash suppressors, etc. Then they were retested with the same ammo lots. NO degradation in accuracy and about a 1% increase in muzzle velocity.

Chrome lined barrels seem to clean up rather easily after a range session. I found the ease of cleaning of Isonite coated barrels to be similar to chrome lined barrels. The Isonite barrels clean up the easiest of any non chrome lined barrels I have ever used. Isonite can be applied to either stainless or chrome molly but the factory needs to know what steel you are sending them because the application process varies a bit. Again, I only have about 2 yr. of cleaning experience with Salt Bath Nitrided barrels. I don't know if the ease of cleaning will continue as the barrels get more rounds on them. Generally speaking, most non coated barrels get harder to clean later in life. Although stainless has a reputation of being corrosion resistant it isn't corrosion proof (I have had plenty of them return pitted) so I coat both my C.M. and my SS barrels. The Isonite on the outside of the stainless barrels cuts reflection down so my shooters like it.

I mentioned flaking of chrome lining inside the bore. Joel Kendrick is my contact at MMi TruTec, the company in Arkansas that does my Salt Bath Nitriding (they call it Isonite). He was mentioning using the Salt Bath Nitriding inside the bore prior to chrome lining it to get a better adhesion. He is currently working with one of the military contractors (maybe F.N., but don't quote me on that) relative to this process. He has given me permission to give out his contact information so I have cc'd him in my reply to you. He can give you the specifics of any testing and evaluation that has been done relative to this process and can give you quotes, etc. should you just be interested in the Isonite by itself as I use it.

One last quick note on chrome lining. Such barrels have the reputation of changing point of impact when heated up. I have found this to be very true. It may be due to the way the different metals (chrome molly and chrome) expand inside the bore. What ever the reason, it does happen and, again, this was verified on a state of the art machine rest. Isonite doesn't exhibit this characteristic.

I am sure you are well aware of some of the things I covered. Lacking specific questions, I just sort of used a shotgun approach which ended up being fairly long. If I left anything unanswered please feel free to get back to me. I have enabled my Spam Blocker to allow your e-mails to come in with out the automated hate responses that Earth Link sends out. I am sure Joel would also be glad to clarify the technical aspects of the Salt Bath Nitriding process. So far I am very pleased with it.

Best of luck!

Butch,
I'm gonna do it. Next barrel I get is going to be chrome moly & it's going to get nitrided.

I'll have to look for a data book with more pages!

Thanks for posting that Butch. Great stuff. A little thread drift here but I want to add that a 1911 gunsmith I know is a big fan of the Ion Bond process for everything BUT a barrel. It has a "rough" finish, at the microscopic level that holds oil better than anything else. This is the opposite of nickel boron, which is so slick putting oil on it is like putting it on a mirror. On a DI AR type weapon all of the oil just quickly blows out of the gun, and when the dust and carbon builds up, it'll jamb.

TAK are you saying avoid nickle boron on a bolt? What about Boron Nitride on a bolt and carrier?

I'm not saying avoid it at all, just be advised that it won't hold oil, and in a hot, dusty environment, you've gotta have oil. I know guys who've done some teaching over at K-SOTIC in Jordan, and some of the clients had those nickel boron bolts/carriers and were the types not noted for weapons maintenance and they had reliability issues with them. Issues that were SOLVED by CLP.

That Nickel stuff might just be the ticket for other environs, I don't know as I've had no experience with them.

I see. This leads me to believe the standard Milspec bolt/carrier is really best overall. I am considering having a 223 upper built using Nitrided barrel, 1-8 twist, and will use the standard bolt and carrier. I was going to get a 6.8SPC but now finding ANY ammunition, shell cases, bullets of any sort is difficult and probably 10X worse with off calibers.

Ion bond, IMO, would be light years ahead of the milspec phosphate on a BC/bolt. The issue stuff can and will rust, Ion bond will not. I am going to send one of mine and have it done soon.

IIRC, DOD stopped chroming bolts because they were cracking. Something called "hydrogen embrittlement", IIRC.

by ion bond you mean salt bath nitriding of the bolt and carrier? Or the boron Nitride?

Parkerizing holds oil.
Chrome bolts cracked due to embrittlement.
The carbon that builds up on the tail of a bolt causes no harm.
Never seen a proper bolt rust.
Chrome lining done right does not hurt accuracy and is good for more rounds than most here will ever fire... combined

I just don't see where the current procedures are lacking.

My last chrome lined barrel was toast at around 6000 rounds. It was a S&W factory barrel. I have no idea if it was done right as it's the only chrome lined barrel I've ever worn out.

I replaced it with a nitrided barrel. I have no idea about the service life of nitride compared to chrome but can say it's resistance to the elements is good. I shoot corrosive ammo out of this rifle exclusively and the bore still looks great. I try to clean it after every outting but sometimes I just don't get around to it for a few days. After I clean the bore looks new. One thing I think is a huge advantage to nitriding over chrome lining is the treatment is in the metal and not on top of it.

FN chrome lines its barrels on their SPR rifles, they are guaranteed 1/2 MOA or better and have a service life of 10,000 rounds.

The belief that chrome lining hurts accuracy is because most chrome lined barrels are utilitarian barrels that aren't accurate from the start.

Corrosive ammo is not that common but it will be interesting to see how yours plays out.