That's most likely a chassis system for remington 700 pattern precision rifles, probably this one from Accuracy International of the UK
AI AICS-AX for remington 700 pattern rifles, available in .308, .300 Winchester and .338 Lapua Magnum
judging from its size and all in porki side, it's probably in .338 Lapua Magnum
read more about it in this article here
The AICS-AX 2.0 chassis, is an updated version of the very popular AICS chassis system (a picture of the original system is at the bottom of the page) from Accuracy International. The AICS-AX fits…
rifleshooter.com
you could say it that it's overall a custom-made performance oriented sniper rifle built on this chassis, quite a clever decision to be honest for getting a custom sniper rifle than tinkering around with existing ones in market - and also shows with these kind of chassis, custom triggers, actions and all how much degree of freedom one can achieve