I've had a couple barrels in the Bartlein #3 contour (heavy sporter) custom cut by bartlein so there was a shoulder on the end that specifically met my suppressor manufacturer's shoulder requirements. Which is .750" shoulder for TBAC. This is the exact same concept as the threaded Barrett fieldcraft. Bartlein charged me an additional 45 bucks for my last one.
I've also just used the $20 adapters and they work just fine, too.
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copy of the description in my invoice from bartlein. I attached the same photo from above to my order.
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