The best budget option for 300 blk - Primary Arms SLx 1-6x24mm Gen III Rifle Scope w/ACSS 300BLK / 7.62x39 Reticle, 30mm Tube, Second Focal Plane (SFP)

This may be the highest performance to price ratio optic available for a .300 BLK, and the ACSS reticle is fast and extremely effective. The glass is clear and crisp, but seems to suffer slightly from barrel distortion around the edges at lower magnifications, but it's slight enough that you won't see it unless you're looking for it and it in no way affects target acquisition.
The magnification change needs a throw lever, and is a little bit stiff, but The included lens caps are adequate albeit no frills, but I did wind up replacing the rear one with a Butler Creek.
Add in the lifetime warranty, and you have a very clear winner.