S&W Melonite coated barrel vs Noveske chrome lined barrel.

[Dirtyboy333]

True. The reason I asked is bc I started a thread on another forum a while back that asked if Sig US 556 barrels are really nitrided like everybody seems to think and some1 had said that they were in fact nitrided and that SIG US used plasma.

I personally hope they are nitrided BUT I don't believe they are bc there is no mention of it on any of the 556 ads and specifications. Couple that with SIG USA's preference for cutting corners and I find it hard to beleive.

I have a problem free 556 and love it but I don't think there's anyway to tell with the naked eye if it is nitrided. Is there?

[SomeOtherGuy]

I have a problem free 556 and love it but I don't think there's anyway to tell with the naked eye if it is nitrided. Is there?

Nitrided carbon steel often looks a bit duller, and the finish seems to have a bit of a translucent look unlike parkerizing which is dull flat at the surface. But this is just a general rule and not something you can be certain of either way from just looking.

Nitrided steel should have a surface hardness of RC60-70 or so and therefore is harder than virtually all knife blades (usually running RC 50-58 depending on the quality and purpose of the blade, with a few as high as 62) and about as hard as a metal file (usually in the range of RC 58 to 64 or so). You could try scratching it with a file - if it scratches easily it definitely isn't nitrided, if it doesn't scratch at all it's most likely nitrided or has some other very hard treatment. Of course this test has cosmetic drawbacks if it turns out not to be nitrided!

[rsilvers]

True. The reason I asked is bc I started a thread on another forum a while back that asked if Sig US 556 barrels are really nitrided like everybody seems to think and some1 had said that they were in fact nitrided and that SIG US used plasma.

I personally hope they are nitrided BUT I don't believe they are bc there is no mention of it on any of the 556 ads and specifications. Couple that with SIG USA's preference for cutting corners and I find it hard to beleive.

Sig 556 rifle barrels made in the US are nitrided. It does not surprise me it is not mentioned in the spec. The ACR also did not mention it in the marketing materials and so people assumed the barrels were untreated.

[WAR FACE]

I'll just leave this here. http://en.wikipedia.org/wiki/Ferritic_nitrocarburizing

[Mjolnir]

Gun magazines have reported that both the ACR and the Sig 556 had nitrocarburized barrels - in fact, all ferrous alloy/steel in the ACR is. Too bad the barrel profile/weight and cost derailed the ACR as the material process specs are impressive.

I don't understand the Marketing Departments. I'd openly tell generically what was done. Nothing can be hidden from fellow engineers with lab equipment anyway. I'd search for and exploit anything that would separate my product line and the rest.

[urbankaos04]

So far, 75 gr Hornady TAP has been the most accurate grouping 9 shots at 1.15", but the 10 th shot opened it up some.

[SomeOtherGuy]

Looks like a great barrel urbankaos. Where did you get it? Is that .750" from chamber to gas block and about 0.700" from gas block forward?

[urbankaos04]

Looks like a great barrel urbankaos. Where did you get it? Is that .750" from chamber to gas block and about 0.700" from gas block forward?

It's 0.776 right before the barrel contour flares out toward the receiver, 0.727 in the middle of the barrel, 0.675 right behind the FSB, 0.750 at the gas block journal and 0.672 from in front of the FSB to the muzzle.

[rfscheer]

Thanks again m4c for a great thread. I especially liked reading that 2nd study of machine gun barrels (the one published in 1967 that compared several inappropriately selected coated barrels with a stellite/chrome setup that Springfield Armory obviously wanted approval for).

I took away that 1960's nitriding technology extended the machine gun schedule of fire lifetime of a 5.56 barrel made of unlined 4150 steel from widely varying 2-12k rounds up to 27-30k.

Why would bargain-tier AR makers use meloniting? Because it's probably the cheapest way to simultaneously provide a nice black finish on the barrel and provide a decent life barrel without corrosion problems in or outside. Does that doom the idea of meloniting? Not to me it doesn't. It only proves that it can be applied at low cost. Nothing wrong with that.

We've been doing our homework and preparing for a test of salt bath nitriding on barrels and other parts coming up soon.

Since salt bath nitriding process temperatures are near 1000F, and the one we're trying is a bit less, I'm most concerned about undoing the previous heat treat of the barrel extension and barrel steel. There seems to be no question that precision barrels (meaning unchromed) will gain a lifetime extension, but it's not clear yet that the side effects are worth it. We shall see.

[nynco]

Correct me if I am wrong, but isn't this what Superior Barrels does to their barrels?

http://www.superiorbarrels.com/

People seem to like their work.