What's special about 1.60 mils and 3.20 mils??

[MikeWhy]

The Leupold CCH reticle has chevrons marked at 1.60 and 3.20 mils left and right of center. See below.

What are these used for? Are 1.6 and 3.2 special in some measurement? Speed, maybe?

Thanks.

 

[hottotrot]

Movers.
2.5mph and 5mph, assuming a quick .308 with a 175gr SMK at ~400yd. Those are basically the speeds of a loaded man walking or a loaded man moving quickly.

In other words, it's a BDC for movers. YMMV

 

[Brians356]

Movers.
2.5mph and 5mph, assuming a quick .308 with a 175gr SMK at ~400yd. Those are basically the speeds of a loaded man walking or a loaded man moving quickly.

In other words, it's a BDC for movers. YMMV

At a particular target range?
-

 

[hottotrot]

At a particular target range?
-

At a particular everything. Shooting a mover is all about time of flight (ToF). The longer a bullet takes to get to a moving target, the greater distance the target will have covered in that time. A shooter would hold in front of the target, assuming that by the time the bullet arrives at the target, the target will have moved into the bullet's path.
The faster or farther the target, the greater the lead must be.This is offset a good bit by the angular nature of Mils or MOA, in that each of those has a greater value at the target with increasing range.

The particular range and the particular speed at which a set reticle feature will be of value varies by bullet, velocity, and atmospheric conditions. You can play with it yourself with JBM Ballistics.

 

[MikeWhy]

Movers.
2.5mph and 5mph, assuming a quick .308 with a 175gr SMK at ~400yd. Those are basically the speeds of a loaded man walking or a loaded man moving quickly.

In other words, it's a BDC for movers. YMMV

Thanks for this. I especially like how well this fits with thinking in mils. For the rest of us, between 5 and 6 MOA is close enough to 1.6 mils for government work.

Heavy'ish, high BC 6.5 Creedmore also finds this a good solution. 1.6 mils is 2.6 mph at 400 yds (0.5 sec. tof). Cosine error for 30 deg. off straight across line of sight makes that a 3 mph walker. Lead a little less for closer; slightly more at farther than 400. For MOA reticles, favor 5 MOA if closer than 400 yds; 6 MOA for the opposite.

Neat!