Originally Posted by
rob_s
Of increasing deviation from the original question...
No, 4140 is not "all that bad", and you are unlikely to notice a material issue. As mentioned, you also already have the barrel and are presumably shooting it and have no immediate problems, so why fix what ain't broke?
However, it IS important to note that the in-spec material is better than 4140, and is not the same as generic 4150 (which also matters, as some makers use the generic). Better enough to run out and change the barrel you're not having any problems with? No. Better enough, at the small price increase, to choose better at the time of initial purchase? Yes.
And finally, as mentioned, for many of us 4140 has become a red flag to other potential problems with the barrel and/or complete gun. Barrel issues tend to be twist (1:9 vs. the more desirable 1:7), chrome lining (many 4140 barrels are not), and chamber (many 4140 barrels are actually .223). Additionally, since 4140 material is less expensive than 4150 CMV, the kinds of makers that tend to use it also tend to cut corners elsewhere. And, as I understand it, 4140 will not pass the military standards for HPT and MPI or would be rejected at such a rate that whatever money the manufacturer was saving would go up in smoke from trashing failed product.
So while I wouldn't opt for a 4140 barrel personally, I think you shoot what you have until it gives you reason to doubt it.