The old-style single heat-treatment left things glass-hard but somewhat brittle. I have seen several that have had the receiver rail shattered by a blow. I have no idea how much force was used, but the guy who showed them to me (in Spokane) also had this idea that Eddystone P-'14 and M-1917 receivers were junk and was destroying every one that came his way..... and it takes a LOT to wreck one of those. Some would only twist, but he scrapped 'em anyway.
Hatcher was Director of Accidents between the Wars. If you wanted to have an accident, you had to get a permit from him..... or maybe it meant that the dead rifle was returned to him. I think likely the latter, as he details each and every documented incident of the rifle failure in his famous "HATCHER'S NOTEBOOK". A couple of hundred failures (or less) out of a couple of million rifles, over a period of 15 years or so, just isn't all that many. Hatcher was trying to be as safe as possible and he was risking nobody's life and limb recklessly. He was reasonably satisfied with the early rifles BUT, once production for World War One got underway, THAT is when things began to slide and the truly dangerous ones started to be made.
The late-type double heat-treated rifles were so FAR superior to the early type that they became the new standard and early rifles with the single heat-treatment became reserve. In stripping early receivers (between the wars, mind you) all that was being done was getting the complete inventory up to the new standard.
There have been a LOT of very-satisfactory rifles built on low-number receivers.
I think (in agreement with Hatcher, who knew a lot more than I ever will) that rate of burn had a good deal to do with straining the questionable receivers beyond their breaking points.
I know where there is a very minty Mark 1 Springfield sitting, right now. It is far beyond my means to purchase but, were I to own the thing, I don't think I could allow it to just sit and look pretty; it would HAVE to be shot. I think I would do this with soft-jacketed bullets (Hornady Spire Point 150s, to be precise) and then I would have to open up one of these tins of 4350 with which I have been blessed.
Knew a fellow once name of John Hall. He was a Canadian, sent by his folks to the USA for university about the time they were talking about a draft here. So he did a year of classes, then the US declared war. He finished out the term, went down and joined the US Marine Corps, went to France and through ALL the dirties. He used a Springfield and had no complaints or comments about them, apart from the fact that it was a good rifle.
I think it must be accepted that the Springfield was, essentially, a good rifle, but that wartime screw-ups with poor manufacturing practices and bad ammunition did a lot to harm its reputation. Sound familiar, Ross Rifle guys?
BTW, I have a couple of rounds of '06 made by National Brass and Copper Tube Co., 1918 (headstamp NC 18) and nothing would convince me that it's completely safe, evcen though a lot of their stuff went 'bang' without blowing up rifles......
Mebbe that's just me...