Magazine assembly to which rifle?

[Promo]

I was given this magazine assembly/trigger housing by a friend of mine. He, as I, has no clue to which rifle it belongs to and asked me for an identification of it. It is made of black aluminum and features inbus head screws, so should be something more modern. the cutout for the magazine is dimensionswise a bit longer than the Steyr Mannlicher Pro Hunter magazine in .300 Win Mag I used for size comparison, so it should be for a larger caliber rifle (.300 WM or something similar). Based on the removeable magazine and the larger round I assume it might be a sniper rifle or a light machine gun.

Attached are some pictures of it. Any help for identification of it would be highly appreciated!

Information

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[Sunray]

"...sniper rifle or a light machine gun..." Magazines are not exclusive to either. Dimensions of the mag well itself would help a bit. The width is as important at the length.
The amount of machining done on that indicates it's more likely commercial rather than military. More of a guess than anything else though.

[Promo]

I‘ve been told it is for an Accuracy International Arctic Warface rifle - can others confirm this?