How important is the scope height measurment?

[rocksolid]

This question is in regard to filling out the requirements of ballistic calculators. I am certainly familiar with garbage in garbage out and want to input information as accurately as possible.

I'm working at being competent at 600 yards I would like to stretch it out to 800 yards. If I'm off by 1/8 of an inch or 1/16 of an inch when does it start to matter?

Right now I feel like I'm doing a bit of eyeballing to come up with a measurement. Should I just go buy a caliper?

 

[mtbullet1]

how accurate do you want to be ?

 

[jimbires]

this is one time close enough is good enough . you can play on JBM ballistics calculator and see for yourself .
https://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

the easiest way to measure scope height on a bolt action rifle is to pull the bolt back until it's even with the scope ocular bell . then measure from the center of the bolt to the center of the scope . fast and easy , no math required . I have a picture of me doing this , but I can't find it now .

 

[jasonco]

You only need be "really close" and not exact. More important to have the bore & reticle square.

 

[lancetkenyon]

Garbage in, garbage out.

 

[jimbires]

I found them , here are the pics

 

[lancetkenyon]

Measure from the front. Center of bore to center of scope bell.
Or....
1. Measure width of scope bell. Divide by 2.
2. Measure width of barrel under front of scope. Divide by 2.
3. Measure gap between barrel and scope bell.
Add 1+2+3=scope above bore.

 

[yobuck]

I just measure from the gas port to the center of the scope knob, or the center of the scope rings.
Realize that much of the information entered for a chart, can and does change due to various conditions.
So you need to do it every time you shoot, or be satisfied with less than perfect information when you shoot.
And it still wont always be perfect based on different wind conditions encountered.
All information gathered for charts should be verified by actual shooting, after which corrections can be made.
Problem with that is that some consider it to be important to always have first round hits. That needs to be clarified, as not everybody considers that being essentual in order to be sucsessfull.

 

[Tangent]

It's not the biggest player, but it's just another variable that we are able to control. I dork-out and use AutoCAD to draft my setups, and just use my calipers to double check measurements in the real world.

 

[rocksolid]

Thanks for all the info. I needed confirmation that I don't need to sweat that 16th of an inch. Those pics that were provided look very similar to me with my tape measure trying to figure out if it was exact enough or not. The video nailed it, the guy said if you're off by a tenth of an inch that's three quarters of an inch at a thousand yards. I can live with that. Thanks again.

 

[yobuck]

Realize that just a very few years ago this entire conversation wouldn't be taking place. Yet lots of people were very successfully shooting long distances. Charts were made and confirmed by actual shooting at the various distances. Then that information was passed along among friends, or in some cases by the gun builder to his customer. Not saying that was better, just saying that it worked, because it required everybody to shoot in order to find out for themselves.
Simply leaving ammo in a vehicle overnight when temps might go below zero will affect the information you have. And with some type powder more than others. Simply leaving a round in a hot chamber due to firing for a period of time could affect a shot.
Regardless as to what we hear and read this is not an exact science,
Serious long range target shooters always confirm their information by using sighter shots, even if they shot earlier on the same day.

 

[Russ661]

If you use a canted rail, say a 20 MOA rail, that means the height above bore is different at each end of the scope. Which measurement would be correct to use or would you add the two together and then divide by 2 to get the height above bore at the center of the scopes length?

 

[BallisticsGuy]

The measurement can be off by a whole .25" and it will make jack all difference to 1000 on guns capable of getting there supersonic. Even being off by a half inch isn't really a big deal given what OP is looking to do.

 

[jimbires]

If you use a canted rail, say a 20 MOA rail, that means the height above bore is different at each end of the scope. Which measurement would be correct to use or would you add the two together and then divide by 2 to get the height above bore at the center of the scopes length?

do yourself a favor and measure the scope height as described in post #3 and #6 , also in the video in post #4 . then measure the scope height as described in post #7 . then run the 2 different numbers in the ballistic calculator linked to in post #3 . you will see an eighth of an inch doesn't really change anything . this is the only measurement that close enough , is good enough