For a 6.5CM practice rifle hitting steel past 500 and out to 1,000 yards on a $500 budget with a precision mil reticle, the sweet spot is the Athlon Argos BTR Gen 2 6-24x50 FFP MIL version.
It’s the one most guys in your spot actually run and like FFP mil reticle that stays true at any magnification, exposed .1 mil turrets with a functional zero stop, side parallax, and illuminated center for low light. Glass is decent for the money clear enough to spot and call hits on steel out to 800–1,000 yards in good conditions not Nightforce level, but way better than basic hunting scopes.
It tracks reliably for practice work and has held up well for a lot of budget long range shooters. The Vortex Diamondback Tactical 6-24x50 FFP is the close runner up slightly better eye relief, Vortex warranty, but most prefer the Argos for the zero stop and illumination at this price.
Grab the MIL version, mount it solid, and you’ll be ringing steel without frustration. If you stretch to $550–600 later, the next jump Viper PST Gen II feels noticeably better, but this will get the job done right now.