Gunsmithing Muzzle threads on 308

[CowboyBart]

I traded into a 308 Win barrel that has 1/2"-28 threads. While this is the same threads that are on my 300 Whisper, are these too small?? I realize the 300 Whisper is lower pressure and volume of gas for subsonic. The pressure might be similar for super sonic, but much less gas volume.
Are 1/2-28 threads OK for super sonic 308 loads?
I can cut and thread 5/8-24 w/o too much effort. 99% of the shooting will be w/o a can. I don't know if a thread protector or muzzle brake will add strength to the muzzle or not. I would rather not "flare" my muzzle, if I can cut and make larger threads now.
I "flared" my muzzle on a Grizzly 45 Win Mag years ago, when I ported the extended barrel. The ports were fine on a 45 ACP, but when I did it to a 45 Win Mag the barrel was toast on the first shot.

 

[Wannashootit]

Far from ideal, but doable if your're diligent on thread form/depth.
I've only done it once on a T3 Lite and customer provided brake he'd already purchased- with the brake manuf's blessing. Like everyone else, 5/8" is preferred and I've got no issues at all with 9/16".

 

[JMGlasgow]

I would say 9/16x24 to be the absolute minimum. I had a hunting rifle in 30-06 threaded by Thunderbeast, they wouldn't go any smaller than that on a 30cal.

 

[Wannashootit]

OP-
Curious, was the rifle factory threaded 1/2"?

 

[CowboyBart]

No. it was threaded that way because I told the previous owner that my 300 Whisper had 1/2-28. He didn't do anything with the barrel, now I have it and want to make a 308 out of it.
Cutting 3/4 of an inch off and making it 5/8-24 is not a big deal. I have access to a lathe.