Can you shoot commercial 308 or is it like the M1 Garand where you have to shoot military loads.
Yes, and that's sort of the irony between the two cartridges.
In .308/7.62 you can shoot most commercial and mil-spec ball loads. With the '06, the "M1 experts" will tell you to stick to shooting only ammo whose velocity and pressure curve is within the original M2 mil FMJ specs; otherwise, you risk trashing the op rod, which renders the weapon unusable other than as a club.
For my M1 Garand, I got an adjustable port so I could shoot commercial. I bought a couple hundreds rounds of 30-06 I was going to shoot before someone told me I had to get military pressure 30-06 or lose an op rod.
No, that's exactly the point of adjustable gas plugs, like the ones from Schuster Mfg. that I have. They allow you to shoot the full range of commercial 30.06 ammo
without damaging the op rod -
provided you tune the gas plug to the particular ammo, or
re-tune it every time you switch to shooting a different load or bullet-weight. That's why a lot of M1 shooters think adj. gas plugs are a PITA, unless you shoot
only one particular load, like a pet handload.
Where the adj plugs are mandatory even with mil-spec .30.06
or .308 ball ammo is on the 16" Mini-Gs that Shuff's makes. Some folks, out of caution, use them in 18" "Tanker" Garands as well. Both the Tankers and Mini-Gs not only have (obviously) shorter barrels, but shorter op rods and op-rod springs too. The Mini-Gs in particular require the use of Wolff's XP Tanker-size op-rod springs which, along with Schuster's adj gas plug, allow you to tame the gas system and, hence, restrict the violence imparted to the op rod and it's reciprocation during firing. Again, you start with the plug fully open (single-shot results), and then simply turn the hex screw in the plug until you achieve reliable cycling of cartridges and the correct ejection pattern, which is spent brass landing at about the 1:30-2:00 location.
All that said, ... with a full-size .30.06 M1 Garand, as long as you stick to mil-spec loads, you're GTG with the normal M1 (non-adj) plug, and a number of ammo-makers (like Federal & PPU/Privy) now make a line of "Garand-safe" FMJ '06 ammo for M1 owners who either don't reload and can't find mil surplus '06. This "commercial" mil-spec ammo allows them to shoot safely in CMP and local Service Rifle matches.
Now it is open all the way so it is a single shot no matter what I shoot.
You can fix that by tuning the plug down to the point where your brass is being consistently ejected out to about the 1:30-2:00 position. That's considered "correct."
HTH.