One of the ways to tell is by looking at it. If the muzzle break has a taper pin through it, then the barrel is a 16 or a 20 inch. This muzzle break can be removed. Gunsmithing is required & there is a chance the barrel could be damaged.
If the barrel has the shiney peel washer behind the muzzle break, you have a 14.5 inch barrel & the muzzle break is welded on. This muzzle break is unable to be removed, because it is welded on.
When these muzzle breaks are installed, they are ment to be permanent & removal of these breaks is discouraged.