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I read around that the SCAR 17S uses a 6061 extruded upper receiver. Does anyone here have any knowledge on the SCAR's upper metallurgy? It seems very strange that the manufacturer of such a high-grade rifle would save a little to not use 7075. I realize these aren't high-wear parts, but with something that is getting thrown around and used by Mil. quite a bit, wouldn't they select a better alloy? 6061 isn't even the best for fatigue as far as I am aware. Any input?
 

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Thanks! Really interesting read. Any idea where people got that 6061 is even used in the SCAR though? If seen it posted around but nothing from FN I've seen. Also, save for corrosion (which anodizing handles well) and weldability it still seems that they went with the 6061 to save on costs primarily. That is perfectly fine if they don't think there needs to be extra strength but are there other advantages I am missing (eg better fatigue, etc) that would make them shy away from something else - say the 7004 which seems to have all the positives of the 6061 and then some?
 

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Thanks! Really interesting read. Any idea where people got that 6061 is even used in the SCAR though? If seen it posted around but nothing from FN I've seen. Also, save for corrosion (which anodizing handles well) and weldability it still seems that they went with the 6061 to save on costs primarily. That is perfectly fine if they don't think there needs to be extra strength but are there other advantages I am missing (eg better fatigue, etc) that would make them shy away from something else - say the 7004 which seems to have all the positives of the 6061 and then some?
They used 6061 because it's extruded. Which in this application is every bit as durable as it would be if it were milled to the same dimensions from billet 7075. The only real difference is milling would take HOURS and a lot of expensive carbide tooling where as extruding takes a minute or two as its spit out of a hot die already at finish dimension (for the most part) with minimal machining needed to finish. The strength gained from starting with a billet of 7075 would be negligible at best but the time/money lost would be extreme.

As as far as corrosion resistance goes, 6061 will still hold up to the elements for a VERY long time before you have any problem there. It's not going to rust away overnight like mild steel. When you hear or read about 7075 being more corrosion resistant, they're usually referring to industrial applications where the material is exposed to various other chemicals that will drastically speed up the corrosion process when used in the manufacturing of other goods.

Im going to go out on a limb and guess that you got the 2025 vs 6061 vs 7075 questions from reading other manufacturers specs on AR 15 type uppers and lowers and the materials they used? Most companies use this sort of thing as part of their marketing strategy to make their product appear superior to the rest in hopes to sell more product. If you compare those materials side by side for torsional stress, shear stress, etc.. The figures you get wont be as drastically different as if you were to compare the same materials with different manufacturing processes such as extrusion vs cast vs billet vs forged.

To sum it up, using extrusion was the logical choice for a tubular upper where as if the lower was also aluminum, it would most likely be machined from either a forging or a billet. Nothing is really going to be gained from using billet 7075 vs extruded 6061 in this particular application. At least not enough to justify the means.
 

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The SCAR upper receiver is not extruded from 6061 alloy. More misinformation generated by speculation from the internet.

7075 can and is extruded regularly, however fine details are not possible and would require secondary machining operations to achieve final required dimensions.

Aluminum oxidizes in a very short time unless it's in a vacuum environment. This skin forms a protective layer of oxidation and is minimal unless exposed to the elements (weather).

The upper receiver carries loads along its linear axis and the only stressed areas... I'll keep that information to myself since my work has been copied far too many times as it is.
 

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The SCAR upper receiver is not extruded from 6061 alloy. More misinformation generated by speculation from the internet.

7075 can and is extruded regularly, however fine details are not possible and would require secondary machining operations to achieve final required dimensions.

Aluminum oxidizes in a very short time unless it's in a vacuum environment. This skin forms a protective layer of oxidation and is minimal unless exposed to the elements (weather).

The upper receiver carries loads along its linear axis and the only stressed areas... I'll keep that information to myself since my work has been copied far too many times as it is.
The upper looked like extrusion to me. Maybe I'll have to get it out tomorrow and take a closer look..
If you're saying it's not extrusion, what would you say it is?
 

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Discussion Starter · #8 ·
Is there any definative info on the actual alloy used by FN? I would assume that since this weapons was designed for evaluation in numerous military trials, there would be info on its composition. What makes you say it's not 6061 STL?
 

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Is there any definative info on the actual alloy used by FN? I would assume that since this weapons was designed for evaluation in numerous military trials, there would be info on its composition. What makes you say it's not 6061 STL?
Im sure its not public but rest assured FN has every cert from every mill and its attached to each serial number of every gun they make. Every gun manufacturer does this. That way if there is a catastrophic failure or any problems whatsoever, the metal can be traced all the way back to the mill that initially made the metal. They know the very exact make up from the mill. I work at a steel distributer so I have to chase around these certs when customers ask for them.
 

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FNH knows what they are doing, in selecting materials.

No need for a stronger alloy. No one has had failure issues with the platform at this point.
 

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I think hes saying it's not extruded 6061 but something else. Pretty sure FN says its extruded
Made in Belgium, the upper receiver of the FN SCAR 17 is constructed of an advanced 7075-T6 forged aluminum alloy, where the lower is synthesized from a durable, lightweight polymer

Champion Firearms | FN SCAR 17S .308 / 7.62
STL apparently does not want to tell you that the same FN upper aluminum alloy was selected for the SEAL because it would only cause a stink storm on this forum and endless debate as to whether having the same alloy lower trigger module as the FN upper really makes a difference in quality, is needless "overkill" or if a cheaper grade of aluminum would be just fine.

Decide for yourself.
 
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If it works for F.N. and the Military, it should be good for all of us here. They did not go the Tonka Toy route when coming up with the Scar Series. Wait the Tonka toys are pretty well made. nevermind. Scar Rifle good. everything else Leave it to the Enemy. I like the Cat poster. funny stuff. RON K.
 

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STL apparently does not want to tell you that the same FN upper aluminum alloy was selected for the SEAL because it would only cause a stink storm on this forum and endless debate as to whether having the same alloy lower trigger module as the FN upper really makes a difference in quality, is needless "overkill" or if a cheaper grade of aluminum would be just fine.

Decide for yourself.
You mean like compared to the plastic OEM trigger module.
 
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