"I was recently talking to a gun designer friend of mine about the materials used in the M1 Garand. The steel, 8620 steel, was the absolute minimum grade of steel that could be satisfactorily used in this application. There were "better' alternatives, I think 4340 would have been a better alternative, and Watertown Arsenal was testing better alternatives in the early 1960's, because the failure rates of M14 receiver bolts and receivers was too high with 8620. The life of a bolt and receiver was stated to be on average less than or equal to 5000 rounds.
I did say, that you cannot fault the material specialists who decided to use 8620 as these rifles are military rifles and they were looking at the beginning of a very big bad war. The previous materials used had a high nickle content, which the US does not have, and still does not have, and has to be transported across oceans filled with Japanese and Nazi submarines, and sharks! 8620 was part of a new series of steels called at the time, National Emergency steels, or triple point steels. Previous nickle steels used 5 lbs of nickle for every 100 pound billet, but the NE steels were using about a half pound of nickle, a half pound of chrome, and a half pound of molybdenum per 100 pound billet. The difference between five pounds and a half pound really adds up over millions of tons of steel! The NE steels gave the same ultimate strengths with a 20% improved yield, over plain carbon steels. And yield is by far the most important characteristic of a steel. These NE steels heat treated consistently through the billet, vastly better than the plain carbon steels used in double heat treat 03's for example. But fatigue lifetimes were similar to carbon steels, or just a little better. Which is OK for a battle rifle.
People have forgot we were averaging 65000 causalities a month in WW2, about 20,000 of those dead, the rest in various states of disassembly. When you are looking at such losses of men and equipment, it is
more important to make a lot of weapons cheap, than build a few very expensive, long lifetime weapons [выделено мной]. The user won't wear the rifle out, he and the rifle will be in shards from artillery, mortar fire, well before the fatigue lifetime of the bolt lugs is approached. So a cheap, just meets requirements steel, such as 8620, is just fine in this application.
But that also means, that hot rod conversions of these actions are very inadvisable. Many have unreasonable expectations about "mil spec" items. You can argue whether the requirements were unrealistic, but once set, parts were not built to exceed requirements, they were built to meet requirements. Money was not spent on a whim, making Garands to the structural limits of belted magnums, for thrill seekers in the year 2017."
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