I buy Green Mountain Barrels for most of my builds. I recently put together my first 300 Blackout using Green Mountain's GM-M41 barrel which has a groove milled for a gas block.

I talked to GM when I ordered it anf the guy on the phone told me that he didn't know who they were made for, or what gas block would work. I had hoped that it would work for the Geissele gas blocks I usually use, but no joy, I just used the set screws without the spring pin.

I'd like to build a couple more uppers for family and friends, so any SWAG's on what gas block this might be for? I did not think to measure where the groove for the spring ping was in relation to the gas port before I assembled the rifle. I'm hoping someone might be familiar with the profile, or have actual firsthand knowledge of who they made it for.

Thanks.

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