Pretty darn sure. Savage used their own proprietary threads for those brakes. The three most common thread pitches are 1/2-28, 9/16-24, and 5/8-24 but Savage went with the 9/16-28 for some reason. My guess is they needed less thread depth to keep enough material thickness on the larger .308" and .338" bores that these were offered on at one time or another.

You will most likely have to either have the end of your barrel lopped off and rethreaded, or call and talk to some of the bigger brake makers and see if they have a tap to make you one special.