Firstly, the Spanish and Latin American Converted Rifles ARE NOT ".308" rifles--- they are 7,62x51 Rifles, for use with Military ammo. Some importers simply stamped ".308" on (Spanish) converts, to facilitate sales in the "non-metric" USA. Notice I did NOT say "7,62 Nato", as Spain originally converted these rifles to use their own 7,62x51 Cetme Cartridge, and the Latin Users did not belong to the "NATO" circle, even though their ammo followed "NATO" Spec for the most part.
Now the actual metallurgy of the various conversions:
Israel... New Barrels to Mauser Kar98k profile, some made by FN, majority made by IMI. NO problems with either Military 7,62 or Commercial .308 Winchester.
Spain: Original Barrels ( M95 and M1916) Bored out, and a complete Liner fitted ( including chamber) and soldered in place. Some barrels show "flaking" of the outer tube from the inner sleeve; but otherwise, the "Tubing" ( Tubado) conversion is Sound, if used with proper Spanish 7,62x51 Ammo.
Any use of US Commercial .308 can lead to Barrel splits, receiver locking shoulder set back, and even cracked bolt lugs in the long term. This includes the FR-7 trainer made from M93/95/16 actions
Advice: use lower pressure Military ammo in Spanish converted rifles, or 80-90% Handloads of Military loads. Avoid commercial .308 ammo if you value your rifle and your physical integrity.
Spanish FR-8 short training rifles: made from M43 (98) Actions, so will be stronger than the M95 and M16 conversions. But originally made to be a "training substitute" in the 1950s, for the newly introduced 7,62 Cetme Assault rifle
( same cartridge, same sighting system, same bayonet and slinging arrangement, same OAL.)
Latin American Conversions: This refers mostly to Chile, but Peru, Brazil, and some other LA countiures converted some Mauser to 7,62mm in the 1950s-60s.
Chile: two types of conversion: For the M95 type Mausers, barrel sleeved by the Spanish method, but with this difference: barrel sleeve only takes up Part of the chamber, the rear being the original &mm chamber; the Joint between sleeve and chamber is soldered, and may become rough enough to cause case extraction problems with heavy use. Otherwise, normal 7,62 Ammo is ok.
For the M1912 Steyr Mausers ( marked "M1912/61" or simply "NATO") the Barrels have been replaced with re-cut Springfield Barrels ( 30/06 chamber shortened and recxut to 7,62x51, and rethreaded to fit Mauser receiver. THis is for the "Short Rifle" version. The rarer "Long rifle" ( 29inch Brl.) Conversion is also a "sleeve" type conversion. (AFAIK).
As these rifles were converted for use as Trainers and Police rifles, they were not made to fire on a heavy basis...more than likely a couple of clips a year, for Qualification, and that's it.
Advice: again, given the diverse nature of the Receiver types ( two lug and three-lug) and the age of the Actions...use low power 7,62 ammo, preferabl;ey 80% handloads.
Brazil: the M968 Mosquete "MosqueFal" 7,62 was made up using new or almost new DWM 1909 Actions, with New-made Barrels in 7,62mm...so any ammo can be used.
Peru: Peru converted a lot of its 7,65 rifles to .30/06, post-WW II...and some of its Short Rifles (FN M32) can also be found in 7.62mm..I have one, and the barrel looks like it has bveen rechambered and slightly set back (ie from 7,65 to 7,62)..the Bore is still 7,65 specs, so any shooting with BT bullets is likely to be less than accurate. Again, these rifles were made of "internal" Training and Policing work, and so would not have had large amounts of ammo through them. IN fact my example ( an FN32) has a bore that is almost brand new. Being a M98 design action, with a "solid" barrel, I would not have any problems with using .308 Commercial, but would prefer not to ( Rifle condition, value etc.).
Other L-A 7,62 conversions...Depends on who did the conversions, and how, and on whjat actions (see above details)
General considerations: on all "7,62" Conversions, whether new Barrel, completely rebored and rechambered barrel, or "Tubada" barrels, I would only use 7,62 Milsurp or Reduced charge Handloads, to the 45,000 CUP level, to match the early 7mm Actions (M93 and 95 types); Only the Israeli and the Brazilian and Spanish FR-8 would I even venture the use of "commercial" .308 ammo.
Regards,
Doc AV