I have a brand new I fired take off barrel in 300 Win Mag 26” fluted, for the Seekins M3 Havak long action. Simply loosen the set screw on your action and switch barrels by hand. It will fit on the 375 H&H that people bought here through Euro Optic or the 7PRC, 7 rem mag, 300 PRC etc…. $525 shipped. Muzzle is threaded but I misplaced the factory radial brake… those brakes suck anyways!