AR10.
Probably too simple a solution for the Military though.
That has already been tried as the M110. It had problems and is to be replaced by the HK G28: https://en.m.wikipedia.org/wiki/M110_Semi-Automatic_Sniper_System
What’s an ar10 today? It can be anything since there is no spec for it. So if they went ar10 like it would be nice if they spec the receivers so, like the ar15, you could have lots of small business provide options and upgrades, swap out caliber, etc. Seems like if they are going to go for a sniper rifle, they would adopt the 6.5 creedmoor round.
That would definitely be recommendation too. The familiar platform will make things easier. aside from that, it’s super accurate.