Dennis Potter sent me a sample of Krupp for the tensile testing study but the source and age was unknown so I didn't think composition analysis would be meaningful. The tensile strength was 113,000 psi.
Composition analysis of a single sample of steel is only meaningful for that one particular heat (or batch) of steel.
There still seems to be a lot of confusion about this matter here. Steel is not an element. It is an alloy, or more accurately, a term to describe a very wide range of different alloys of iron and other elements. It is like trying to describe bread without differentiating all of the different varieties and recipes and methods for baking bread. Even two different batches of bread, using the same ingredients and baked by the same cook, can have a slightly different taste and texture. And because of the wider range of purity in the ingredients making up any particular heat of steel, it is far more difficult to replicate the composition of different heats of steel than it is for a baker making different batches of bread.
Pre-WWII Krupp steel mills mainly utilized Bessemer and Siemens-Martin processes. The Siemens-Martin Open Hearth process was slower than Bessemer Converters, but more controllable. What made their steel famous and highly regarded was mostly the same things that gave Eskiltunas, Solingen, Bohler and others their own stellar reputations. And that is the quality and purity of their ingredients, the recipe or composition, the process used to make it, and the attention to details like time, temperature, degassing, removal of impurities, etc. Even the composition of the fire-brick used to line the furnaces can affect the quality and final product. All of that is a function of the men who make it and the management who decide to invest in better materials and processes. So like baking bread, two different Melters (The guy in charge of the furnace operations) using the same ingredients and the same recipe in the same oven can and do have slightly different outcomes.
Even the same Melter producing consecutive heats of the same product order can have a different outcome. For example, if a heat calls for 20 tons of automotive scrap, some of those scrap cars may contain contaminants such as lead, copper, or other unseen materials that can affect the final product, or even cause an entire heat to be discarded or utilized for something else than what the customer wanted. There are radiation detectors in steel mills to detect radioactive scrap which could contaminate an entire heat. At the integrated steel mill where I once worked, I saw them opening baled scrap cars with dynamite because they noticed an increase in slag production from the L-D BOF and Electric Furnace operations They found that a scrap dealer was filling up cars with broken cement, drywall gypsum, and other garbage before baling to increase weight. This is why quality steelmakers have their own in-house Met Labs to test every heat during the melt, and after the heat is poured, hot rolled, cold rolled, pickled, annealed, and processed. Crappy steelmakers such as found in China and Taiwan are not as concerned with the composition and attention to detail or testing.
The steel Krupp marketed to gun makers for shotgun barrels is probably quite different than Krupp steel intended for railroad rails, ship hulls, or structural I-beams. It is possible, and even likely, that different barrel makers who used Krupp steel utilized different grades of Krupp fluid steel, and it isn't all the same stuff. And when we see "Siemens-Martin Steel" on a set of shotgun barrels, that does not mean those tube or the steel used to produce them came from some Siemens-Martin Steel Mill... rather, it means they were produced by some mill that utilized the Siemens-Martin Open Hearth process. Because of that, metallurgical testing of a set of barrels stamped "Siemens-Martin" may tell us almost nothing about another set with the same mark. It is merely a marketing term to tell us how it was made, but not who made it, what ingredients it contains, or ultimate strength or purity.
