mxsailor803, I've no idea where you got the idea that 30 caliber Garands use reduced loads compared to commercial loads with SAAMI specs for peak pressure and/or velocity. Same for the 7.62 NATO Garands used by the USAF and USN for service or competition. Both rounds have had the same MIL-SPEC pressure limits at 50,000 cup since their inception. And both versions have had thousands of commercial ammo, either .30-06 or .308 Win. fired in the respective ones without issue. SAAMI specs for .30-06 are the same as MIL-SPECs as far as pressure's concerned. And for the 7.62 and .308 rounds, the specs are close enough, SAAMI's 52,000 cup, and there's no danger using either in a 7.62 Garand.
There were no reliability issues in the USN and USAF converted 30 caliber Garands to 7.62 NATO by just replacing the barrel. In the initial stages, it was noted that the port pressure of the NATO round was lower than the 30 caliber one, so the barrel's gas port had to be drilled out a bit on the barrels made at Springfield Armory in MA. In service use, there were no problems.
For 30 caliber Garands that had the chamber insert installed, there were issues. Sometimes those inserts came out with the ejected case. This idea was quickly scrapped. The USN Small Arms Match Conditioning Unit (SAMCU) sold all their chamber inserts to some commercial outfit for retail. So only those CMP 7.62 NATO Garands with the original Springfield Armory 7.62 NATO barrel should be considered safe to fire. Check out this page for details:
Here's the straight scoop on CMP's sales of 7.62 versions:
Scroll down to the section titled: "Navy M1 Garand Barreled Receivers"
Accuracy wise, the 7.62 Garands were hands down more accurate than the 30 caliber ones. Their 1:12 twist barrels were better suited for 150-gr. ball and 172-gr. match ammo's bullets. The 30 caliber ones 1:10 twist was way too fast for best accuracy. This is one reason why the targets used in competition and training had their scoring rings reduced 3 years after the NATO round was first used in matches in 1963. Commercial match ammo was tyically more accurate than military match stuff. The USN SAMCU air gauged all the 7.62 barrels they got from Springfield Armory and those with groove diameters uniform and at .3076" to .3079" were set aside for match versions for the USN Rifle Team. They easily shot commercial match ammo into 4 inches at 600 yards; no 30 caliber match grade Garand ever came close to that.