# Scope/Bore height measurement

Discussion in 'Long Range Hunting & Shooting' started by mtnwrunner, Feb 28, 2012.

1. ### mtnwrunnerWell-Known Member

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Okay, may be a stupid question but in any case, I don't currently know the answer.

When you measure the scope height above the bore, where do you take the measurement from on the scope? Reason that I am asking is if there is a additional MOA rail on the gun, that obviously lowers the front objective so do you take it there, the middle or the rear of the scope?? I'd like to be as precise as possible for turrent specs.

Randy

2. ### 4xforfunWell-Known Member

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Here is a simple and EXACT way to measure.

1) You need the diameter of your action. I'll save you some time...if it is rem 700 or clone, it is 1.35". Anyway...figure 1/2 that (radius) and write it down. (.68")

2) You need to find the diameter of your scope TUBE (not the objective or occular ends). I'll save you some more time.... a 1" tube is obviously 1", a 30MM tube is 1.18". You need to find 1/2 of that (again..radius) lets use the 30mm...1.18 divide by 2 = .59". Write that number down.

3) measure your ring/bases from the BOTTOM of the ring where the scope sits to the bottom of the base where it contacts the action serface. lets say that this is .75".

Now, simply add them up....... .68 + .59 + .75 = 2.02".

Now, FORGET about the tapered ring bases....it does not matter which base you measure unless you are ULTRA ANAL....(like me ) Then you simply measure BOTH the front and rear ring/base...add them together, and divide by two and add that number to the action radius and and the scope tube radius. But, I'll save you even some more time just pick one and use that number, because we are talking fractions of an inch at 1000 yards.

Good luck,
Tod

3. ### mtnwrunnerWell-Known Member

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Tod, that looks easy enough.
So, what i am reading is that you are thinking that it doesn't really matter if the front objective is lower than the rear eyepiece??
And yes, we are all probably anal---isn't that why we are here???

Thanks!

Randy

4. ### 4xforfunWell-Known Member

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I have never measured the difference between them, but it can't be any more than ten to twenty thou difference. So, in my above numbers it could be either .020 more ore less....so 2.00" or 2.04 inches.

Meaningless.

Do you have your ring/base close by. If so, measure the difference between the front and back and post the results. I'm kinda curious.

5. ### mtnwrunnerWell-Known Member

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Well, just for grins I did measure the distance between the rear and front of the base.
Rear is .506 and the front is .418.

Randy

6. ### rscott5028Well-Known Member

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Being precise is good and necessary.

But, there are other errors and variability that creep in and stack up such as scope tracking, errors in BC calculation, or variability of BC from bullet to bullet/lot to lot, up/down wind drafts, vertical component of spin drift with varying rifling styles/specs.

Ultimately, you need a starting point that's good enough and then have to shoot to confirm your drops.

-- richard

7. ### 4xforfunWell-Known Member

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Wow...88 thou (.088).

I did the math. 300 grn sierra at 2800. 2.5" height = 220.4 in low with a 300 yard zero. A 2.59" sight height = 219.83 low with same 300 yard zero.

We are talkin 1/2 inch (1/20th moa) at 1000 yards.

Like I said... a non issue, all though less of a non issue than I had originaly had thought.

8. ### mtnwrunnerWell-Known Member

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Well, that is cool---now I can sleep at night................
I think I'll measure from the middle and call it good.

Thanks,

Randy