Virtually the only ones that regularly put an O-ring ahead of the threads like that, are Spyder barrels.
It's possible it could be an older, obscure one like Spartan or Brass eagle Cobra, but those are either unlikely or VERY
unlikely. (I'm not sure even Smart Parts, back in the earliest days of barrel making, made one for the Cobra.)
Even money it's Spyder.
And boy, to I need to update that barrel page.