I saw a u-tube video that did not recommend 4140 steel for barrels. What does that mean for the m& p 10 which I believe does use this steel?

It is not as good as some of the other barrels out there but only applies if you do a heck of a lot of shooting. For the average person, it's a none issue.

4140 has been used for decades + for firearms barrels and has been more than up to the task. If I liked a firearm enough to buy it, 4140 would not be i disqualifier.
Jim

If you are not doing mag dumps, the 4140 is good. A very high volume shooter might have need of the 4150.

removed . . .

I always like to think of how much money I will have spent on ammo in order to wear out a barrel. Hint: It's *way* more than the cost of a $200 - $300 barrel.

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- Fourth Horseman -

If you stay interested long enough to wear it out, then look at a nitrided barrel which will last even longer.

The M&P barrels are nitrided, unless they have changed since introduction.

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Cliff
CCSO, FPD ret, USN ret.

A 4150 steel barrel has a slightly higher carbon content making the steel slightly harder than that of a 4140 barrel. Ideally a 4150 barrel should last longer and stand up to a little more abuse, but the average shooter will do just fine with the 4140 barrel.

Even Century Arms' cheap AK has upgraded barrel from 4140 to 4150 steel...

I get the impression that many here don't know what "Nitriding" does to steel. S&W Nitrides the barrels (inside and out) causing the steel to be extremely hard and rust-proof. Discussions of barrel steels are pretty much moot when barrels are Nitrided.
Machine gun barrels are Nitrided for durability.
Do yourself a favor and look up Nitrocarburizing or Nitriding on Wikipedia.

I like these comparisons between 4140 and 4150 steel.....very friggn good steel (4140) for firearms vs a little bit better than that steel (4150)

Actually, many machine gun barrels have stellite lining. Look at the price tags for M2 variant barrels.

Per the former commander of the USAMTU, buy nitrided for an accuracy edge. Hard chrome lined for rapid fire use.