Zero for BDC scope on 556

[voyager9 3,434]

I recently purchased a vortex crossfire 3-9 scope with the BDC reticle. I'm hoping to get to the range soon to zero it and that got me thinking the "best zero".

 

I prefer the 50/200 zero and it's what I use for my red dot, mainly because it's +/- 1.4 inches from POI out to 225 yards or so. I'm not sure this works for the BDC reticle since it does not have the pips above POA for a hold-under. It seems a BDC is only good when the zero requires only a hold-over. Is that right? From the charts I've seen only the 100yd zero applies and that drops way off after 225.

 

Would I be better off going with a zero appropriate for a BDC reticle, or being consistent across my rifles and ignoring (or only using when hold-over) the BDC?

[Displaced Texan 11,731]

What are the graduations of the BDC, and how is it calibrated?

 

For example, a TA-31F ACOG is calibrated in 100m increments, for M855 ball, out of a 14.5" barrel. You dial in at 100m, then the graduations of the reticle get you on at 200, 300, on out to 800m.

 

Your sight in distance depends on how your reticle is calibrated.

[Vlad G 345]

So vortex has a manual for that reticle: http://www.vortexoptics.com/uploads/web_manual_reticle_bdc-sfp-13a.pdf

 

I would follow their recommendation for the varmint cartridge that .223 is.

 

They recommend 200 yard zero, with the hashmarks being 300, 450, 550, and 650 for the top of the post.

 

The other way to do it is to use a ballistic calculator like Ballistic (iphone) or Strelok (android), chrono your ammo out of your gun, and then play with the data to see what the hash marks mean depending on the drop of your ammo.

 

Let me show how I would decide. The drops for the reticle are 1.5, 4.5, 7.5 and 11 moa (top of post)

 

Lets say we are using my gun and ammo for the maths, and the ammo is 68gr Horandy, at 2850fps, I also know that my scope center line is 2.7" over the muzzle line (this matters, most good scope mounts on a AR with a 30mm tube are 2.7, but you have a 1" tube so you need to check)

 

If I choose a 200yard zero, the hashes will correspond to 265, 360, 450, 530 (give or take). With 100yard zero my drops would be 210, 325, 410, 500.

 

So .. for my SPECIFIC ammo/barrel/scope height/etc I would pick the 100yard zero as the hashes would be close to 200/300/400/500 to be useful to me and easy to remember instead of the ones for the 200 yard zero.

 

For your ammo and your barrel you will have to kinda decide for yourself.

[voyager9 3,434]

Thanks vlad! I think the thing I missed when reading the manual is that the BDC reticle is really only used beyond the 200yd zero. I was overthinking it and trying to figure out if/how it's used 50-200yd with hold-under.