Yeah I've seen a few other 223's that were large shanks and sporter weight barrels. They were model 16's with a left hand action. I figured the same thing, that they just put them together with what ever was on hand at the time. Oh forgot to mention the LRP too. It's also large shank in standard size calibers. Of course it is a variant of the model 12. I have one of the 116's in 375 Ruger. It's large shank and a pretty sweet rifle.