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For the Good ol' US of A rifles, yes
Ours are Walther (Germany) or Sassen Engineering (UK)
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As far as I know, for the UK Barrels, AI has used Lothar Walther (not related to the gunmaker Walther), these were the most common on the AW rifles. They have also used Border Barrels which were bought out and have now moved to Birmingham and are called Sassen Engineering. They also had a few Australian barrels made by a company called Mad dog. You can tell which are which by serial number. AI UK used to be able to tell you if you phoned them up which barrel you have.
For the US they were primarily Bartlein, chambered by Dave Tooley.
More recently, the AI North America owner and the US Importer (Scott) teamed up with AI owner Tom Irwin to create the barrel company WIN Tactical. As far as I know they also use, or did use Bartlein blanks.
I have barrels made by all listed in various configs spread over my AI collection.
My favorite, my newest one, AI AXMC in .338LM with a WIN Tactical barrel.
I love the AI, and the buyer from the OP has a great rifle! I'd love an AW with the serial number range he'll be getting as it'll be an instant collectors piece.