Another height over bore check

[The Harbor Master]

Ok, this almost doesn't need to be its own thread but just need to double check... I have a T3x Superlite with Nightforce 2.5-10x42 mounted in Hawkins Precision "UltraLight Tactical" rings (lows), on a 20moa Area419 picatinny mount (bonded to action). I am having a hard time getting a solid scope height for entering into ballistic calculators. All the methods for measuring I've seem a little imprecise or difficult to squeeze calipers into weird angles (most likely just me).

Here are the 3 ways I've attempted measuring:

Using calipers, measured from bottom edge of ejection port to what I can best eyeball to be center of scope tube. I'm getting 1.865" as my height over bore, a bit higher than I thought.

I then measured from bottom of ejection port to the top of the picatinny mount (comes to 1.037") then added the 0.885" that Hawkins states to be the low rings' measurement from picatinny base to optical center. This gives me 1.922" height over bore. Even higher than I thought.

Lastly, I measured the diameter of scope tube and got 1.182", then divided that in half to give me the center line (0.591"). Next I measured bottom of ejection port to underside of scope tube and got 1.363". Adding half the scope tube diameter and the measurement from bottom of port to bottom of scope gives me 1.954".

Does anyone have the same or a close set up to confirm these measurements, or advice on getting it accurate? And yes, I am aware that it's not going to make a massive difference if I'm slightly off, especially at my comfortable hunting range (450yds and in). I can probably just use 1.93" and call it a day. I just enjoy the minutae of all this stuff, even it drives me crazy.

Thanks in advance, I feel my place in this forum has become to ask the stupid questions so other noobs won't have to

 

[mxgsfmdpx]

Measure your scope with it un-mounted in the rings and mark a center line on the rifle ejection side of the tube.

Measure from bottom of ejection port to your mark. Done.

You could use all 3 of the different numbers you mentioned above and won’t be able to shoot the difference out past 1,000 yards.

 

[BLJ]

I measure form the center of the over pressure port to the center of the rings.

 

[SomeJackassOnAForum]

Pull bolt back so bolt face is under mounting area of tube. Measure from firing pin hole to bottom of maintube. Add 0.6. Recognize that the level of precision required for this task is to measure to 1/10th inch.

At this point your number is 1.9".

 

[Dave Thomas]

I use a ruler and measure from center of scope tube to center of bolt. As long as you're close you'll be good.

 

[schmidty3]

One way to do it..

like your last method....

But do it to the bolt as well.

If you know the diameter of the scope, and the diameter of the bolt. Take the calipers, Measure from the OD of the bolt to the OD of the scope (the bottom of the bolt to the top of the scope). Then subtract the radius dimension of each!

 

[BLJ]

Using a 75 ELDM with a MV of 2900 in a generic calculator.

Scope at 2.5” above center bore is 2.1 MIL at 450.
Scope at 2” above center bore is 2.2 MIL at 450.
Scope at 1.5” above center bore is 2.3 MIL at 450.

59*/29.93/78%/1k’ for weather.

 

[BBob]

As already pointed out it’s not that critical. Like all you need is: “eyeball it ruler precision” Go ahead and plug in some values and see how much it changes the outcome. You might be surprised at how little difference it makes.