Night Vision Halo XRF Optical Center, Height above bore for thermals.

[shields shtr]

Kind of an offshoot to the zero thread, but it got me thinking. I called up Nvision and asked them how they figure out their height above bore. The tech on the phone said that their optical center is 39mm. Of course, I stupidly hung up the phone and then thought after "I wonder if that is the optical center of the unit (which makes the most sense to me", or what they use to calculate the height above bore? Obviously, this measurement will vary.

Any tips or common numbers folks use? I am using the stock mount that came with the unit and have it mounted on a Defiance action with a 20moa rail. Caliber is 6 creed. I am thinking to calculate I use 1/2 bullet diameter+rail thickness+mount thickness+39mm?

 

[Jumper]

I have almost the exact same setup; XRF with Bobro offset mount on a 6mm creedmoor, 20moa rail, ARchimedes action. I just took careful measurements with my calipers. Mine is 2.88" above bore. Interestingly my other rifle with a steiner M7 scope on it is 2.90".

Its not that critical to have exactly accurate measurement. I doubt you would ever notice the difference if you were off by a tenth of an inch.

 

[shields shtr]

I have almost the exact same setup; XRF with Bobro offset mount on a 6mm creedmoor, 20moa rail, ARchimedes action. I just took careful measurements with my calipers. Mine is 2.88" above bore. Interestingly my other rifle with a steiner M7 scope on it is 2.90".

Its not that critical to have exactly accurate measurement. I doubt you would ever notice the difference if you were off by a tenth of an inch.

Awesome. Thanks for the reply, this is what I was hoping for. When I took the measurements I ended up with 2.7". I do know that tenths don't make much of a difference, but I had 1.5" plugged into my ballistic calculator and the 1.2" difference was substantial. I airballed a few coyotes last night at about 300 yards and realized I was shooting about a foot high with the zero I had calculated.

 

[Jumper]

I just zero'd mine a few days ago. I'm shooting a 105gr Barnes matchburner and I zero'd mine 1.7" high at 100yds. At ~ 3000fps, this should let me hold dead on out to 375yds on a coyote. I figure 375 yards and in is a reasonable expectation where I hunt. Also, I recommend using the TH zero method with a good thermal target. Im confident in my zero on this rifle now for the first time. Now I just have to find time to go hunting.