It would be for a hunting rifle with a skinny sporter profile barrel. The general rule I have read for 90* shoulders is they have to be .100" larger than the major diameter of the thread, as in .725" for 5/8. It sounds like using a Sig taper and this new DT adapter of yours opens up more possibilities for thinner barrels. If a .675" barrel OD will get full taper engagement into your adapter, that's a win.