Shooting Range in Vegas sharing info on what works and what doesn't...

[Defaultmp3]

As an update, a guy I know received a chopped off portion of an MR556 barrel (left over from an SBR conversion project) and looked at it under high magnification, and did not observe any white layer, which is highly suggestive of no nitriding of the bore. Combined with Montrala's statements, I think it's safe to say that the MR556's keyholing failures at Battlefield Vegas should not be blamed on the weaknesses of nitriding as compared to chrome lining.

[lysander]

As an update, a guy I know received a chopped off portion of an MR556 barrel (left over from an SBR conversion project) and looked at it under high magnification, and did not observe any white layer, which is highly suggestive of no nitriding of the bore. Combined with Montrala's statements, I think it's safe to say that the MR556's keyholing failures at Battlefield Vegas should not be blamed on the weaknesses of nitriding as compared to chrome lining.

You wouldn't find any white layer after the barrel has been used. The nitride layer is destroyed by the combination of heat and erosion.

There are a few studies on this.

Also, some nitriding processes require the white layer to be removed.

[SomeOtherGuy]

You wouldn't find any white layer after the barrel has been used. The nitride layer is destroyed by the combination of heat and erosion.

I don't think defaultmp3 said what the round count was for that portion of the barrel resulting from an SBR conversion. It might be zero for all we know.

Even if it has some round count, how quickly would the far end of the barrel towards the muzzle lose its nitriding layer from use? The fastest rate of erosion is at the throat, and it diminishes away from the throat.

[lysander]

I don't think defaultmp3 said what the round count was for that portion of the barrel resulting from an SBR conversion. It might be zero for all we know.

Even if it has some round count, how quickly would the far end of the barrel towards the muzzle lose its nitriding layer from use? The fastest rate of erosion is at the throat, and it diminishes away from the throat.

The white layer can be removed by mechanical abrasion or through heat, and it is typically only a few microns thick.

Generally, the white layer is considered an undesirable feature.

[Defaultmp3]

You wouldn't find any white layer after the barrel has been used. The nitride layer is destroyed by the combination of heat and erosion.

There are a few studies on this.

Also, some nitriding processes require the white layer to be removed.

Interesting, I did not know that. I'll ask my source to see if he can do a hardness test, then.

However, as SomeOtherGuy noted, the barrel portion was from the muzzle, which I would think to have fairly little wear compared to the throat. It is my understanding that while the barrel was not brand new, the round count was quite low, and the gun had not been run hard.

Either way, I stand by my statement that blaming nitriding for the keyholing issue is not sound, given the conflicting information on the barrel.

[lysander]

From an Army report on nitrided barrels:

Nitride case hardening has been applied to all barrels surfaces including the interior diameter (ID), outer diameter (OD), and the gas port bore. The white layer and case hardening are evident throughout the barrel. These are particularly evident in the Location 4 metallographic images, see Figure 2.

A uniform white layer was present through the barrel. The thickness was measured at locations 2 and 5 and averaged 9.8 ± 1.4 μm (0.00039 ± 0.00006 in) where the stated uncertainty corresponds to one standard deviation (σ ) of the measured average.

The hard and brittle white layer is of a concern. This layer may spall during operation, entraining abrasive particles in the bullet/gas stream and leaving bore surface asperities. Complete removal of an average thickness white layer from the bore during firing would result in a diameter increase of 20 μm. The manufacturing drawing for the similar M16 barrel (ARDEC DWG 9349054, 8 November 2002) specifies a maximum 25 μm variance in the bore diameter, putting a barrel with a removed white layer very close to exceeding specifications. Partial removal of the white layer due to firing is expected to negatively influence system accuracy. Reduction or complete removal this layer during manufacturing is highly recommended.

From what I understand, most barrels are nitrided by salt bath or other methods that minimize or eliminate the white layer for the reason noted above.

[dramabeats]

MR's are SA only. So unless they drilled the hole converted it, this gun wasn't shot on FA.

C4


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All of the guns he discusses in that thread are full auto. It's the allure of their business.

[pinzgauer]

All of the guns he discusses in that thread are full auto. It's the allure of their business.

Wonder f they operate under a "dealer sample" type license or what?

I've forgotten how the various licenses work.

[dramabeats]

Wonder f they operate under a "dealer sample" type license or what?

I've forgotten how the various licenses work.

It would be too expensive for them to not do that

Otherwise they wouldn't have a SAW (theres only like 1 or two that are transferable) or a m134

[pinzgauer]

It would be too expensive for them to not do that

Otherwise they wouldn't have a SAW (theres only like 1 or two that are transferable) or a m134

I knew it would not be transferable stuff, just wondered if the dealer sample allowed retail rentals.