Nick Jenkinson, a UK air rifle champion, designed the Hawke SR6 and SR12 special reticles for air rifles and subsonic rimfires. You can use them for any type of rifle and the free Hawke software lets you dial in your scope reticle without a lot of wasted ammo.
I found my SR6 reticle worked perfectly with my BSA Lonestar .25 cal and Baracuda pellets when zeroed at 50 yards and JSB Exact pellet when zeroed at 60 yards. Each slash in the Christmas Tree downward from crosshairs represented an increase of 10 yards almost perfectly. This is at 6X power, but a slower or faster bullet would work if you changed the power accordingly. Use lower power for slower bullets and higher power for faster bullets. The SR 12 reticle works best around 12X, so it is for target/varmint work. For general hunting, especially night hunting, the SR6 reticle is best.
I got my Hawke 3-12x50 scope on sale from E. Arthur Brown Co. for under $200. It has red illuminated reticle that works MUCH better than the cheap Leapers scopes. I gave away my Leapers scope, it was so aggravating.
You are ahead of the game if you use a scope with a reticle designed for an air rifle. The common firearm ballistic reticles don't have enough aiming points. Also, adjustable parallax is an absolute must for accurate air rifle work.
The Hawke scope also has a ranging device that is useful on prairie dogs. It's faster than using a laser rangefinder, and with average sized prairie dogs quite accurate. I use the laser RF to find the true distance, than note where the PD fits in the scale of the scope rangefinder. After a while you don't need the laser RF out to 100 yards if a PD is out of his hole. If making head shots, then I use the laser RF. Vertical drop is critical on head shots, but not on standing PD's. Wind is a far greater problem with standing PD's at distance.
Hawke scopes work great on air rifles because air rifles are a big deal in the UK and Hawke is a UK company. None of our scope companies care diddly squat about air rifles, you will not find a single air rifle reticle in the Burris or Leupold line. The best you can do is the mil-dot or standard ballistic reticle.
Twiddling knobs is too slow for air rifle work, and there is much more holdover in air rifles than in firearms. You will be twidding the elevation knob for many more turns than if you used a faster firearm. Get a proper air rifle ballistic reticle and you are way ahead of the game if hunting. Target knobs work best in target work, not in the hunting field where fast response is needed.