poliorcetes said:

Are we totally sure that M7 is going to be fielded in numbers as an "assault" rifle?

I am not totally sure that NGSW will be fielded at all.    But, the stated plan is to field the M7 as a replacement for the M4 in the infantry and some other close combat elements.

Interesting video.

He mentions ~5:30 zone that SIG uses 'Maraging steel' for superior barrel life. Curious what alloy that is and what properties.

https://en.wikipedia.org/wiki/Maraging_steel

Some discussion of it:

https://www.practicalmachinist.com/forum/threads/maraging-steel-for-us-civilians.195118/

Googling Maraging steels, came across this, from the makers of the H&K416's awesome barrels:

https://www.aubertduval.com/wp-media/uploads/2022/01/BD_fiche-petits-calibres_012022.pdf

No idea if this is the alloy, but description seems relevant:

And then this super fancy Italian shotgun also claims to use miraging steel, likely just for the bragging rights.

https://www.bosis.com/shotgun-basis-models/challenger/challenger-technical-detail.html

gatnerd said:

Curious what alloy that is and what properties.

These are very low carbon highly alloyed steels with high strength and ductility after heat treatment.
Maraging means "martensitic" and "aging".
A typical maraging steel is: X 3 NiCoMoTi 18-9-5
Allmost no carbon but lots of Nickel, Molybdenium and Titan

These alloyes are nothing new really. But they are pretty expensive and the required heat treatment could not be done by anyone in the past. This has changed in the last decades so the availability and price got better. Which means its now more commonly used. Its still not common but its also not obscure anymore.

Maraging steel has been around a long time.  I recall that it was used on the NASA Lunar Lander in the 1960's and has long been used for the tail hooks of carrier aircraft.  

I cannot resist to add that 32 CrMoV 12 10, the steel of HK416 "awesome barrels", had been the steel for G3 barrels for decades and one can order commercial barrels using it from Lothar Walther, for example.     

JPeelen said:

I cannot resist to add that 32 CrMoV 12 10, the steel of HK416 "awesome barrels", had been the steel for G3 barrels for decades and one can order commercial barrels using it from Lothar Walther

Ah, very cool.

It seems super fancy to us in the US, because virtually all gun barrels here are pretty boring 4150cmv barrel steel. 'Premium' is having the barrel Cold Hammer Forged (standard practice in europe forever), as opposed to button rifled. (also part of why the majority of my collection is made in Europe)

The standard M4 of the US army is just button rifled 4150cmv, chrome lined, and reportedly starts to see accuracy degradation at 6-7k rounds. A good 4150 CHF barrel is hoped to go to 20k rounds. 

Meanwhile this 416 is still holding 4moa after 67,000 rounds:

https://soldiersystems.net/2013/03/30/canipe-correspondence-retiring-my-416/

I recall Emeric also reporting great results with France's 416 barrel testing.

....

Kind of random, do you happen to know what barrel steel Steyr uses for the AUG? 

In the US they had been using FN made CHF barrels, but reportedly they are now using Austrian blanks that are just finished in the US (a peculiarity of our import laws here.) If they're using the same / similar barrel steel to the 416/G3, I may have to snag an extra barrel. 

gatnerd said:

The standard M4 of the US army is just button rifled 4150cmv, chrome lined, and reportedly starts to see accuracy degradation at 6-7k rounds. A good 4150 CHF barrel is hoped to go to 20k rounds. Meanwhile this 416 is still holding 4moa after 67,000 rounds:

The 1970s era soviet AKM cal hold the 4 MOA after 25-30K rounds of steel-jacketed military issue ball ammo, provided it was maintained properly

the AK-74 is expected to have a minimum barrel life of 10K rounds with mix of 1 tracer to 4 ball rounds; in real life, you can get between 15 and 20K ball rounds trough the '74 before it starts keyholing, and that's with the steel-jacketed 5.45 ammo which is much more unforgiving to the barrels than the brass-jacketed 5.56

and IIRC the standard barrel steel there is the equivalent of the German 41CrMo4 steel or US 4140, and the barrels are cold hammer forged since the 1970s

Great to info, thank you.

It definitely seems cold hammer forging plays an important role in barrel life.

The M4 won’t start keyholing at 6-7k rounds, but rather that’s when accuracy and velocity starts to decrease outside of spec.

Whats frustrating is this is largely due to the M4 TDP not being updated. 
 

FN had the contract for M4s for a while, and had to button rifle them, despite FN being known for their CHF production (they are a huge OEM for barrels in the US). This created a bizzare situation where all military M4s were button rifled, while all of FNs civilian AR15 barrels were CHF.

mpopenker said:

and IIRC the standard barrel steel there is the equivalent of the German 41CrMo4 steel

This steel is nothing special at all. Its a pretty common steel for tools and general mechanical construction. Quality bicycle parts are often made from it for example.