A Winchester M70 Varmint HB in .222 Rem. Bought it new in '76, and added a Leupold 12X as funds allowed.
It introduced me to varminting, which hangs with me to this day. The first day I had it out, I sighted it in at 175 yards at a home made range we had set up at a friends ranch.
After shooting about 10 shots to get it into the bull, then a lovely tight group, I was letting the barrel cool and glassing my target, thrilled. Lo and behold, there was a gopher standing up about 5-10 yards to the left of the target, and probably 20 yards further out. I put the cross hair on him, squeezed off, and he disappeared instantly.
No way I got him, I thought, way too far out.
Went and changed the target later, and walked out to see if I could find him, and.......there he was, nailed. I became a varminter that day.
Sold it in 1991, been missing it since....1992.