[wunhunglo]

With the gas sleeve fully forward/closed & gas plug open, it should be chucking those cases miles, so there is definitely a problem there. Have you tried swapping the gas piston from your .30-06? Do you have any way of checking the piston/cylinder clearances with both rifles for comparison?
Some thick grease in the piston ring grooves might make it work once or twice & that will tell you if the clearances are too great.
With it blowing off the front handguard I am wondering if the gas block was not properly fitted to the barrel. It should have been pressed on then soldered, maybe the solder has failed and allowing gas blow by??

Just reread your bit below, even with the gas shut off, it still blows the handguard off?? If that is the case I strongly suspect the barrel/gas block sealing.
If I set the gas port block to "off" and fire it manually cycled, it ejects just fine, but still I have the hand guard issue.