1. What size is the gas port?
2. Was the barrel pre-dimpled for use with a gas block or was the block already installed?
3. Don't assume it is the gas tube.
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The barrel is not dimpled. The gas block used two set screws on the bottom of it. The port on the gas block is larger than the one in the barrel.
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Those pics don't do much. But, if the barrel isn't dimpled then the gas block was most likely not set correctly. A .078 port should be sufficient so my feeling is that you need to have the barrel dimpled properly, and then set the gas block (I also recommend Loctite 271 on the screws) and that will most likely solve it.
Ok, I'm buying a dimpling jig tonight.
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Make sure the gas port will line up with the gas block hole before dimpling. I had a gas port that was mis-located on one barrel and had to take a bit off the back of the gas block to get it to align
Personally, I'd unpin the MD and remove the gas block completely so good measurements can be made to ensure proper alignment with the gas port.