Originally Posted by
OlongJohnson
Ugh. I strongly suspect "entirely tool steel" is misinformation. I have seen "ordnance steel," "ordnance-certified alloy," and even "ordnance-certified tool steel" elsewhere, as well as discussion that the material is the same used in artillery - although without stating for what parts, as that information, as well as any details of what the actual alloy is, are considered protected (or whatever level of "non-public" applies) information. It all reads to me like people repeating stuff they don't remember quite right but sounds good and they don't understand in any case.
I would be surprised to learn from a reliable source that the whole frame and barrel are actually made of something that would be classified as "tool steel," although we do like triggers and hammers made of appropriately selected and processed tool steel. There is extensive discussion out there about various members of the 4000-series family of chromoly steels and their uses and differences when used as gun barrels. It would seem reasonable that the MR73 barrel would be made from a very high quality barrel steel (one used for artillery barrels, even, which may be different than those used for target rifle barrels), and that the frame might be made from the same material.
It's not 100 percent obvious that it would be optimum to make the frames and barrels out of the exact same alloy. At a first pass, special ordering one type of material from the foundry is better than ordering two, but if the forms are different (e.g., round bars for hammer forged barrels and flat plate for forging blanks or billet frames), they might be separate orders or production runs in any case. Knowing how much aluminum my former employer had to order at once (and well over a year in advance) to get the foundry to process it to the required specs, and given the estimate that Chapuis may build only about 400 MR73s per year, it seems likely that an order of steel, if it is a special-ordered production run, will fill all the production requirements for several years. Maybe more than several.
I would bet two P-F bucks that whatever the alloy is, it's closer to what you'd see a top-quality target rifle barrel made from than it is anything classified as "tool steel."
Another part that might be tool steel is the pivot pins. We know they are a different material than the frame, as they do not react to the bluing salts in the same way, hence the "spotted" look analogous to but far less pronounced than the steel pins in an anodized scandium S&W frame. An alloy classified as tool steel would likely be an appropriate choice for the pins, as extreme wear resistance is a desirable characteristic there, so trading some toughness (accepting greater brittleness) for additional hardness could be useful.
Full disclosure: you stepped on a pet peeve:
"Tool steel," like "aircraft aluminum," is a fairly general category description, kind of like "the color blue." There are a multitude of chemistries in both categories. The actual physical properties of any given chemistry depend very heavily on its manufacturing history, and the wide range of end states is applied as required to optimize the results of each part application. Advertising that something is made of "aircraft aluminum" doesn't tell someone who knows something very much at all, and probably isn't even a legitimate claim in most cases (at least to someone competent in specifying/building/inspecting aircraft).
Older production guns are around, if you are patient. Some of the cheaper ones you'll see around are police trade-ins from various sources, possibly beaten on, neglected and abused in various African countries. Some are nicely preserved. Prices will vary accordingly. There were a handful of engineering changes through the years. I'm not aware of any of them being considered "cheapening" in the way that later S&W "dash" numbers generally are. As a shooter, I'd want the leaf-type hand spring, which is the later version. I've read that Chapuis has continued using the same alloy that Manurhin used for frames and barrels. The guns are now made at least partly with CNC equipment, which obviously was not available in 1973. It is generally considered that CNC equipment, properly used, will if nothing else achieve the same (or better) precision in less time at lower cost with reduced chance of errors. CNC equipment, improperly used, can also make pallets of bad parts at the speed of a computer.
Some people seem to be of the opinion that older guns are nicer, others report having inspected both and found more recent Chapuis guns to be the best ever made. Collecting is a different game, but I have not seen a preponderance of opinion that the best shooter will be had by getting an older gun. MR73s are not like Korths where the design has evolved through periods of significant engineering differences since the 1960s. My general expectation is that variation within the different MR73 populations is likely to exceed the variation between the averages of the different populations (except that the lower-priced "mass" imported guns with rough service histories are likely to be in the worst shape). In other words, which gun you get is likely more important than when it was made or in which factory. That is particularly true of any machine built with a great deal of hand fitting and hand finishing. A single Pierre may very well have better and worse days, and Guillaume may be more or less skilled and conscientious than Pierre, which could also vary by day.
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