.22LR General Ballistics Discussion:
Slowing through the speed of sound can make a bullet unstable. With typical centerfire cartridges, this happens at such a long range that it’s rarely an issue. With rimfire cartridges, it can be, even at shorter ranges. The speed of sound varies with ambient conditions and is approximately a function of elevation:
The next chart compares zeroing options for subsonic and supersonic .22LR. It’s convenient to use a Zero Offset at a desired midrange for zeroing. The offset prevents the POA from being shot away while shooting the group. The amount of offset should be ~50% of typical target size. Practical .22LR zeroing choices are 0.5″-1.5″ high at 50yds. For longer range shots, (>130yds), subsonic ammo can offer more accuracy and quieter retort. The slower subsonic bullet drops about 2.5″ more at 100yds but because it doesn’t suffer the shock of transitioning from supersonic to subsonic velocity, the ballistics should be more predictable.
- For important shorter ranges, the scope tube height above the barrel influences the calculations quite a bit so make sure you use your appropriate value.
- Benefits to setting your zero some amount high at the midrange:
- Your POA does not get blown away while you are shooting your group.
- For hunting, the amount high you select is related to your target size such that it creates a range in which you can point and shoot and still be on target.
- The bigger Zero Offset you can use, the wider range your POI offset will work, plus the less MOA adjustment required at longer ranges.
- I zero my .22LR rifle 1″ high at 50 yards. I usually shoot the same supersonic ammo in my rifle as I do in my handgun. Per the charts, my +/-1″ range is 18-86 yards and at 100yds I need 2.7 moa which is just a little less than the first mildot reticle holdoff.
Optics Discussion for .22LR
- Adjustable Parallax is useful to keep the 50 yard zero group tighter. I usually shoot the OptiCo 3.5-10x50mm SFP with fixed 100yd parallax on my .22LR. If I don’t pay attention to center my eye in the reticle, it can open my 50yd group up ~0.5″. That issue goes away towards 100yds where I am very confident. At 150yds, shooting supersonic ammo, I hit a 6″ square target about 80% of the time. 125yds is about the range to which I’m very confident with ~6″ targets.
- For longer range shooting, I recommend Adjustable Parallax and quality ammo. With good ammo and the OptiCo 4-14x44mm FFP Adjustable Parallax, my confidence extends beyond 150 yards. The FFP reticle is 0.17 moa wide so at ~200yds it will be ~0.35″ wide on typical 4″-6″ size targets.