Once you get the gas block off, stick the shanks of number drills in the gas port. Let us know what the size is of the largest drill bit that fits.
Based on what he's said, that steel case ammo functions but brass cased ammo does not, it doesn't really sound like a gas pressure / volume issue.
If there's enough gas to extract & eject the steel case, it would seem likely to be enough gas for the brass case ammo, absent some other contributing factor like the rough chamber...............maybe.
Really hard to get an answer from the crystal ball w/o see the gun.
If you ever get it figured out, report back with results.
MM
