I would heed what others have said, however if you can find a decent or nice Chilean in original 7mm they can shoot good like many other contract mausers. 2 inch groups or slightly more at 100 yds with factory ammo is what mine averages. Here is mine. I also won't get one unless it has a matching serial on bolt and receiver.
However your questions brings to mind a 1916 Spanish mauser I bought over 10 years ago and after reading on the net the possible dangers it has just sat there. It is a CAI import marked .308 on the barrel. I didn't pay much for it would like to shoot it but I am leery to. My understanding is don't shoot .308 in a 7.62x51 unlike the opposite don't shoot 5.56 in a .223 maybe someone can verify that.
I might just go to a milsurp dealer I know one day and see what he will put toward it to a trade on another Mosin or Enfield if it is indeed questionable to shoot.
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Regarding your Spanish .308/7.62, there are a bunch of THR threads that deal with the issue. One, is whether these were fired with only a cartridge called the 7.62 CETME which was used in the earliest versions of the Spanish CETME rifle (they could not handle full bore 7.62 NATO). I would not be surprised if that was so or not. From at least a Guardia manual dated 1968, they did fire these with 7.62 NATO (the Guardia is combination police and national guard in Spain).
Like the 1895, the 1893 dated from a time where steel technology was fairly new and while outside craftsmanship was high due to the cheap price of labor, mass steel production techniques was not fully mature. The Mausers used the simplest form, carbon steel, because of its advantages in machining, cost, greatest knowledge circa 1890's about the metallurgy for heat treatment, and to give the requisite toughness to the steel for longevity. Nickel steel was just beginning to be used in U.S. commercial firearms at the time but militaries throughout the world are notorious penny pinchers and conservative regarding new fangled inventions.
Mauser refined his work from the 1889 and 91 versions, the 93-96 versions, and then his masterpiece m98. We see consistently better gas handling for example in the 98 compared with the earlier 89-96 versions, the 98 is a stronger design, and is easier to disassemble the bolt for cleaning and so forth. Nevertheless, the design is case hardened steel--the receiver would be machined while still soft (to save wear on machine tools) and then case hardened (heat treated) through being exposed to a carbon source at high temperatures for a set time in a furnace. The carbon impregnated the surface giving these rifles the hard glossy finish and slick feeling when handling the bolt.
But, it is possible to go to far, if the temperature range is not correct for case hardening or the duration of heat treatment was off, (or some impurities in the steel can also do it) you could either get burnt steel (coarse and weak due to its crystalline structure)
https://www.scribd.com/document/164168730/Overheated-and-Burnt-Steel, insufficient case hardening--softer than spec steel, or brittle steel (very strong but the receiver is hardened all the way through and these can shatter like glass due to sudden impact). For a laymen's purposes, this article describes some of the processes involved,
http://www.anvilfire.com/article.php?bodyName=/FAQs/heattreating.htm
Not as well publicized as low numbered Springfields, but there are accounts of Mauser receivers going kaboom just from problems of heat treatment. For that reason, proof testing was used to weed out the bad ones but the proof testing was based off of the lower pressures of the original ammo (depending on the country and cartridge around 40-45 k psi) and then ". . . the Gunmakers will take the mean service pressure specified for a particular cartridge, and add an additional 25% on top of that. Within the ballistics calculations, they come up with exactly how much extra powder is required to produce 25% more pressure."
https://www.thefirearmblog.com/blog/2014/08/29/show-proof/
Thus, proof loads for these early Mausers ranged to around 50,000 to 56-57,000 psi. Later, as machine gun ammo became hotter and the technology better, the issued ammo pressures for later cartridges went up to the higher end of 45000-50000 psi with a corresponding increase in proof loads. But being the notorious cheap skates that most militaries are due to budget pressures, they kept the older rifles for purposes like "war reserve" etc.
Now, compare this to 7.62 NATO or .308 Winchester specs and make your decision. One fly in the ointment is that the Military chambers often have a longer throat and larger chambers as in the 5.56 in order to lessen pressures, ease extraction, and allow firing ammo in less than factory new condition. Unless you do a chamber cast, you really will not know what kind of throat you have. Another issue on many of those 7.62 Spanish Mauser conversions is that they wiped out the arsenal information so you do not know when and who made it. Some Spanish Mausers made during the Civil War are notably inferior for example in quality and obviously early Spanish ones are more likely to demonstrate varying quality as well as the processes were not quite refined yet.
A Spanish Mauser probably won't fail catastrophically absent a large scale gas event or an overloaded cartridge but what you will see with repeated firings is gradual lug setback in the receiver (headspace gets longer, extraction becomes difficult, bolt becomes hard to manipulate, short brass life, etc.) Personally, if I did fire one, I would use only once fired cases of a known origin with the loads well below the max. Using cast boolits would also help do so. In the weaker U.S. 7x57 factory ammo, I have few qualms other than obviously paying attention to safety equipment and how the rifle is performing. These are not the rifles you want to use for high round counts.
