I have one I bought used when I was home on leave from the Navy in 1968. It was the receiver sight model and it has a 4 digit serial number. I had wanted one since they first came out and I'd seen the Ruger ads, something to the effect that, "This is the 5 pound carbine that will put its 240 grain bullet through a 6" pine tree and still kill a deer". The ads with the guy showing the gorilla he'd killed with one really cemented my lust for it. I never got to do anything with it until I returned from SEA in the early '70's. Accuracy was always disappointing, even though I shot Norma's "Carbine Load" ammo in it. I did kill some deer with it however, it was perfect for hunting in the woods, on foot as we used to always do. Eventually I read an article in Rifle magazine about accurizing it. I discovered the stock through-bolt to the rear receiver nest was loose so I tightened that and glass-bedded the gas block. After that treatment, with a 1-4 Bushnell Banner, it would shoot under 2" at 100 yards. Later I put an Aimpoint red dot on it with which I killed probably the biggest bodied deer I ever killed at 200 yards. It sits in the safe at my son's house now. I should get it and put it back into service.
