Just using a cheap old tape it looks like about 5/8". The barrel looks like 21" just measuring from the outside and 1.5-2" will need to be cut off to get past the screws for the sights I'm assuming.
I guess I’m going to be the dissenting vote here?
I’m only going to give an uneducated opinion because I don’t know this for fact. But if you’re barrel muzzle is 5/8 of an inch without cutting the barrel shorter and possibly back into a thicker section I don’t think you’ve got enough thickness to thread the barrel?
I’ve seen the engineering drawing for a couple of different silencer manufacturers and they have a minimum muzzle diameter of .7 inches or greater. This is assuming 5/8” x 24 threads per inch.
I guess I would contact your suppressor manufacturer and ask them if a half-inch by whatever thread pitch would work with your caliber rifle.
Physically it will work. Just not sure if it’s recommended for actually.
(Recommended being the keyword by the way)
I’ve got a few AR barrels that are a bit under the minimum muzzle diameter for 5/8” thread pitch and have never had any issues.
I think that minimum diameter recommendation is for there to be enough shoulder for the suppressor to seats squarely against.
Some folks are not comfortable deviating from recommendations is the only reason I’m floating this out here.