Here is the recent, and now locked, thread
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=561800

The (probably pre-1920) Model 12 Nickel Steel barrel is non-standard (just slightly low nickel at 3.17%, standard is 3.25-3.75%; and slightly low manganese) AISI 2340 medium carbon low alloy steel.
C - .39% (.38-.43)
Mn - .65% (.7-.9)
Sulfur and Phosphorus both < .04%
Cr - .08%
Mo - <0.01%

Here's the WOW
Yield strength - 100,000 psi
Ultimate tensile strength - 124,000 psi
% elongation - 19

I found an industrial standard tensile strength for 2340 of 94,275 psi so the barrel may have had some form of heat treatment?

Thanks again to Channing.
And BTW I've got a section of Lefever DS Dura Nitro barrel coming

Winchester Nickel Steel was introduced for the Model 1894 rifle about 1896; with a reported ultimate tensile strength of 100,000 - 108,000 psi with an elastic limit of 81,000 psi.

Winchester “Gun Barrel Nickel Steel” for rifles was surely different that the nickel steel used in shotgun barrels
“Report of Heat Treatment of Barrel Steel Rolling”, 1902
http://books.google.com/books?id=YzhUAAAAIAAJ&pg=PA181&lpg
From Bethlehem Steel Co.
Carbon - .50%
Manganese - .77%
Phosphorus - .026%
Sulphur - .037%
Nickel - 4.0%
Chromium <.01%
Molybdenum <.01%
Tensile Strength - 107,000 psi

Midvale Steel Company c.1900 Nickel Steel
Carbon - .59%
Manganese - .765%
Phosphorus - .027%
Sulphur - .03%
Nickel - 1.57%
Chromium - .065%

The analysis would confirm Mike Hunter's statement
https://winchestercollector.org/forum/general-discussions-questions/receiver-steel/
“Winchester’s Nickle Steel had 3 1/2 % nickel and .30%-.40% carbon. I know that Winchester sourced this steel from the Midvale and Crucible Steel Companies.”

Thankyou Dr. Drew. Imagine....truth in advertising! Winchester had and still has legions of fans. Sadly, mostly for their earlier products. Still...impressive.

Yep. Winchester Nickel steel..."about twice as much tensile strength as ordinary steel"
If referring to "cold rolled" Winchester Standard Ordnance (decarbonized) steel that is correct

Winchester introduced the Model 1894 rifle in 1894, chambered in either .38-55 or .32-40. In 1895 1894 was chambered first for the .30WCF & then the .25-35, both with Nickel Steel barrels "Especially for Smokeless Powder". The .32 Win Special followed in 1902.

The .30-40 Krag was the first cartridge introduced in America as a Smokeless round which had not been preceded in a black powder loading.

The .30WCF was the first Sporting rifle cartridge introduced as strictly a Smokeless powder round. It has been duly recorded & known for some 125 years now that this occurred in "1895".

Just came across this

Colonel Charles Askins, The Shotgunner’s Book, A Modern Encyclopedia, 1958
https://archive.org/details/Shotgunners_Book_The_A_Modern_Encyclopedia/page/n27/mode/2up

The Yankees who made sportsmen nickel steel-conscious, with typical reticence, never revealed the contents of their alloy; but it was generally
Carbon .35% - .45%
Manganese .50% - .80%
Phosphorus maximum not over .04%
Sulfphur about the same
Nickel from about 3.1% to 3.75%.

Our specimen
Carbon .39%
Nickel 3.17%
Manganese .65%

Good post, Drew. Thanks.