scope height from barrel centre

[sauer]

ok guys im thinking bout trying longer range plinking etc. im a long range novice!

 

i have the chrono , the scope with relevant turrets, and a couple of different ballistics programs for the iphone

 

isnipe & bullet flight

 

anyhow ...how do i measure the distance from barrel center to scope centre ...... i can do it roughly but was wondering if there was any "method" that you guys use etc

 

also i remember someone on here posted a link to an article form some american military guy who teaches....it was an article on longe range and explained moa real simply etc......

 

anyone know the one i mean or link to it~?

 

 

cheers

guys

 

 

Sauer / paul

[Ronin]

Its centre of bore line to centre of scope tube.

 

 

Makes a big difference to ballistic programmes if you get the measurement wrong (at long range)

 

 

Measure as close as you can and if possible input into your prog as accurately as possible.

[pat]

You will need the correct measurement device(s)....

 

Vernier calipers will get you most of the way there :

 

1) Choose a point along the barrel where you can measure both the barrel O/D and the objective bell O/D

2) Measure the barrel O/D and divide by 2, this will give you centre line of bore to outside of barrel

3) Measure the objective bell and divide by 2, this will give you centre line of scope to outside of scope

4) Measure the distance between barrel and scope. This is a little trickier unless you have some LONG reach calipers, but failing that you can use a pack of playing cards, notepad etc, just keep adjusting the thickness until it is a snug fit in the gap, then measure cards / pad with the calipers.

5) Add up the three measurements to get centre of bore to centre of scope. Note that this will not work with mounts that have built in tilt (eg a 20 MOA rail). You'll need a bit of trigonometry to work it out properly if you have that type of mount.

 

The result should be accurate enough for most purposes, it will be within a few thousandths of an inch

 

Cheers,

 

Pat.

[1967spud]

in reality the best place to measure it is at the reticle as this is where the adjustment will come from if you go to far forward and say your scope was on a 20moa rail the mesurement will be out all be it a little but as ronin has stated it's all relative at range

[Barrelsniffer]

in reality the best place to measure it is at the reticle as this is where the adjustment will come from if you go to far forward and say your scope was on a 20moa rail the mesurement will be out all be it a little but as ronin has stated it's all relative at range

 

 

I was told another way

 

Measure your bolt width...and then half it ??

 

Measure the top part of the action just above where the bolt sits....

 

Measure dist between action and bottom of scope tube...NOT OBJ LENS

 

Then measure Scope Tube body at turret area...and again half it

 

Then add up..not forgetting to half what parts were measured to get answer..??

 

This is how i do mine

 

Mick

[Jay Foxing]

I have always measured from the scope ring split to the firing pin on the open bolt, i find this accurate enough.

All the best,

Jay.

[onehole]

Mmmmmm!!? some interesting methods,I just use calipers from a visual centre of scope tube to visual centre of the barrel.There are a few places you can take this measurement and check for a good reading.

Not an answer to your original question but in addition I think its worth remembering that ballistic programmes only work well when you have a spot on zero,some do this at 100yds/meters which is simply too short and the trajectory at this point is much too flat. You can be as much or more than a whole MOA out at 200 and this will escalate the further you go out.

Good luck Paul,but personally I would work with a 200 yard zero in the field and I think you will find your longer shots a little closer to your ballistic programs predictions.Even then you will probably fudge something to make your program match what actually happens out in the field.You also need PERFECT conditions[rare as rocking horse poo!]

All the best.

[Lee]

I have always measured from the scope ring split to the firing pin on the open bolt, i find this accurate enough.

All the best,

Jay.

 

Jay, you may get caught out one day doing that, not all scope rings are split in the middle.

 

Lee

[Scotch_egg]

This should be a sticky IMHO.

[Jay Foxing]

Your right Lee, my Warn rings at the moment have a split top vertically not horizontally. But lets be honest, most are split centrally. And out to 500yds (i don't shoot much further) a .5moa rifle, balistic programs are not going no notice if you have got your mesurement out by a couple of mm. But saying that, your program is only as accurate as the information you feed into it.

All the best,

Jay.

 

Jay, you may get caught out one day doing that, not all scope rings are split in the middle.

 

Lee

[sauer]

guys as usual, helped me out again!!!!!

 

thats what i love bout this site, plenty experienced folks willing to share & help

 

and the fact it doesnt appear to get hijacked by majority of nobbers !!!

 

 

like other sites do

 

 

thanks again

 

 

anyone remember the article or link that was on here regarding MOA? it was written by some US military/marine sniper teacher but explained things real well / easy

 

 

thanks agian

Sauer /paul

[auquhollie]

Paul,

Just remember the single most important piece of date you must remember is your height above sea level. This will make a big difference if you just fudge it.

 

Ads...

[pat]

MOA (Minute of Angle) is quite easy, just gotta remember what the maths teacher told you at school :D

 

There are 360 degrees in a circle.

There are 60 minutes in a degree, so 21600 in a circle.

Now remember that the circumference of a circle is given by "two times PI times R" where R is the radius.

 

OK, that's the basics so let's put that to work:

 

Imagine you're in the middle of a big circle and that this circle has a radius, R, of 100yds, ie you're at the centre of this imaginary circle and your target is on its circumference. If you were to walk all the way round the circumference then you'de travel 2 * PI * 100 (yards) = 628.3185 yards. You'de also have gone round a complete 360 degrees. So 360 degrees, or 21600 minutes equals 628.3185 yards. So how far is one minute ? Simply divide by 21600 and you get 0.0290888 yards. That's not a very useful number! Fortunately, there are 3 feet in a yard and 12 inches in a foot, so there are 36 inches in a yard, and if we multiply by this then we get 1.047 inches. This is quite close to 1" so the usual "rule of thumb" that 1MOA is 1" at 100yds. Of course that is only an approximation and the extra 0.047" can accumulate once you start talking about a 10 MOA move... there is a tangible difference between 10" and 10.47" (about half an inch, LOL).

 

Unfortunately, MOA isn't a particularly "useful" quantity since it isn't "exact". This is where the milliradian comes in....

 

Remember that the circumference of a circle is 2 * PI * R. Half the circumference would be 1/2 of that or just PI * R. So we can use fractions of the circumference to work out how far round we go for any given angle. But what if we could work it out directly ? Enter the radian. Like the degree, it is also a unit of angular measurement, but instead of there being 360 degrees in a full circle, there are 6.283185 radians. Well, that's not a very friendly number for doing maths in your head.... or so it seems... because it is precisely 2 * PI. This has the useful property that if you travel 2 * PI radians round the circumference then you've gone all the way round, and have covered a distance of 2 * PI * R. The 2 * PI is common to both. What this means is that if you go X radians round a circle of radius R you'll have covered a distance of X * R. Now that IS useful! Let's say that R is 1000 metres. And let's say we move 1/1000th of a radian round it then we'de have moved 1/1000 * 1000 = 1 metre. In other words, if we move 1 milliradian (as in 1/1000th of a radian) then at a distance of 1000 metres that would be 1 metre. At 100 metres it would be 10cm. One milliradian is always precisely one thousandth of the radius, ie distance to target. It also works for yards but it's a little less obvious: 1 mrad at 1000yds is still 1 yard. So far so good, but most people talk of 100yds, at which point it is, like the metric version, still 0.1 yards, but there are no "centiyards" so it isn't 10 centiyards, it is 3.6 inches, or one tenth of the 36 inches that make up a yard. This also happens to be the same as 3.437 MOA.

 

At the end of the day, neither system is superior in being able to place a bullet where you want, if your chart is in MOA and you follow it, it will work. Likewise if it's in mrad it will work. If your reticle has stadia at regular intervals and is FFP and you can see how far off you were, you can correct easily using either system. It just gets a little confusing when the reticle is a MIL dot (one dot every mrad or 3.437 MOA) and the turrets are in 1/4 MOA....

 

Hope this helps more than it confuses,

 

Pat.