The 512 is a tube fed .22 rifle. The 513 is a mag fed rifle. The 514 is a single shot rifle. All very good .22 rifles!
You forgot about the 510 single shot, and the 511 mag fed rifles.
OP ....... It’s probably a 512-X, the X series rifles had sights that were very similar to, if not the same as, the sights on the Nylon series rifles. I also believe that the X series rifles all had grooved receivers, not the case for the pre-X series rifles.
