WARNIN

Spanish "7,62" is NOT Nato and Less ".308"
Again this Misinformation (propagated by the original Importers back in the 1980s) about these M1916 and other Converted Spanish Mausers.
The M95 and M1916 Spanish Mausers converted to "7,62x51" chamber, were for the Lower Power, Spanish developed 7,62 CETME cartridge...same cartridge dimensions, different bullet and most importantly, pressure factor.
The Rifles were converted for both Police("Guardia Civil") and Army training use. Some were left in their (original) configuration, but some (the "FR-7") were converted to a CETME Rifle look-alike, as far as sights, etc, was concerned ( FR-7 === Fusil Reformado, 7mm original, or ex-Mauser Small ring --M95 and M16 models).
When they were sold off, the "7,62" mark of Spanish Ordnance was MISINTERPRETED by the US Importers to be ".308", and the added ".308" marking applied.
So everyone MISTAKENLY believes they are suitable for both Military 7,62 Nato and Commercial .308 Win. Ammo.
Whilst the rifles concerned will stand up to occasional use with such ammo, the nature of the Bolt design and the sometimes assumed "softness" of the Receiver steel, leads to Locking Lug setback and excessive headspace. Some suffer already from this malady from "New" due to Inadvertent use with full Power 7,62 Nato ammo in Spain, after they made the switch from CETME ammo to Nato, in the 1970s
My advice if you have any Spanish "7,62" marked Spanish Mauser Rifle of the M93/95/1916 design (Small Ring receiver, two lug bolt) that it be Handloaded loaded with 40,000PSI level loads, in cartridge cases sized with Military spec sizing dimensions (NOT ".308" commercial dimensions) and ex-Military cases used (thicker walls). Current production Lake City cases are fine. ( The original 7mm receiver was set for 45,000 PSI max. Loads)
If your "Spanish Mauser" is a M43 derivation ( "Model 98 action, large Ring") then it is fine for "7,62 Nato/.308 W" ammo, although I still would keep to Milspec ammo and leave the higher pressure Commercial ammo alone.
Kornhauser's Booklet on Gunsmithing the (Spanish) Mausers makes good notes on the internal and metallic problems of Spanish Mausers...since a lot of the 7mm versions were actually built during the Spanish Civil War, by sometimes quite basic factories, their overall quality control did suffer...those made before WW I were quite well made, and followed German quality practices ( as propounded by the Licensor, L. Loewe/DWM).
Best regards,
Doc AV
AV Ballistics Technical Services
Brisbane Australia
I picked up several thousand bullets, pulled from CETME cases that had corrosive/Berdan primers that were faulty.
The powder was still OK and the bullets are .311 in diameter and weigh 112 grains.
The bullets have exposed lead bases and are the same length as 150-grain fmj nato bullets. The length is achieved by the use of a polymer plug in the nose to fill the cavity in front of the lead base.
OP, your rifle was rebarreled and chambered for the CETME round which was developed by a tech company for Spain when they decided to rearm with a full auto rifle, that has the company CETME name and is very similar to the later HK91/93 rifles, with very little effort the mags are interchangeable. All were derived from the roller retarded blowback design of the Stg45.
The folks stating the round was loaded with lower pressures are correct.
This came about after design changes were made to the CETME rifles, which were originally chambered for the 7.92x57 and later for the 7.92x33 and 7.92x45(Spanish design)
When the Spanish finally settled on a cartridge around 1980, it was decided to go with the 7.62 Nato and many of their M58 CETME rifles were modified to handle the slightly higher pressures.
Here's where the fly in the ointment with any rifles chambered for the 7.62CETME round comes into play.
The Spanish experimented with several bullet weights, lengths and types before settling on the Standard Nato round.
This can lead to all sorts of confusion and in some rifles, such as the one in your pic, maybe a catastrophic failure, but if you're lucky, maybe only lug recess setback.
I've seen several of the Model 1916 rifles, which the one in your pic appears to be and is manufactured to a maximum working pressure standard of 46,000CUP (copper units of pressure)
These rifles will likely be OK for some of the higher pressure 308Win factory loads but a steady diet of them will eventually set back the lug recesses in the receiver and maybe on the bolt lugs.
I've only seen one 1916 receiver with lug recess set back. The owner bought the rifle as a "custom" sporter and proceeded to load the cartridges to the nuts.
He's lucky the only result was lug recess set back. Stretched cases were his first warning.
Most Spanish rifles based on the M93 design are pretty well made, not all. The model 1916 rifles all seem to be well made, especially if they bear the Oviedo stamp.
I won't say 308 Win factory rounds will damage or cause a catastrophic failure in your rifle, but is it worth taking the chance???