Scope Height

[sammass]

Downloaded a ballistic calculator. In the setup, it asks for the scope height, which was defined in the FAQ's as "Distance between center line of scope and center line of bore."

Concept is simple enough. But without out all the fancy machined or electronic gizmos, is there a simple method of determining the distance?

Thanks in advance.

[Sleighter]

A ruler?

[sammass]

:-) TY, Sleighter... You suggested of course the obvious.

I also had a similar thought although it would take two folks to easily accomplish: one to hold the ruler approx. centerline of the muzzle, while the shooter nestled into the scope, focusing on the ruler. Somewhat dodgy when they calculate in mm's. The other minor issue is the fuzzy mess caused by the short distance of 20" from objective to crown, a bit less than the minimum focus distance.

I had hoped there might be another option. But thanks for the suggestion.

[Sleighter]

I think that you're way overthinking this. Hold the ruler alongside the scope at the objective end and measure from the middle of the bell to the middle of the barrel. There's no need to measure from the muzzle end of the barrel or to look through the scope for that matter. Just use the portion of the barrel that falls underneath the objective of the scope. The middle of the barrel is the same at any point on the barrel.

[Merc1138]

You could do it the simple way(just using a ruler or some calipers and eyeballing it). Or you could do it the "I like to claim I have OCD and want to overthink everything and do it the difficult way), which doesn't require 2 people. It does require a dowel, something long enough to measure with, and an understanding of the pythagorean theorem.

Using a dowel to fit into the end of the bore(use wood or something), find the center point, run a line back to the center of the scope, this will be "C". Then run another line from the point you started with on the dowel and stop at a point where you can meet the end of "C" on the scope with a 90 degree angle, this will be "B". "A" is now the short line between the ends of "B" and "C". By the time you've finished reading this, and realized you can solve for "A", you could have just eyeballed it a half dozen times and been close enough, and probably wasted half an hour trying to measure that.

Instead of worrying about trying to get that measurement to be exact for a ballistic calculator that will not actually be exact for your rifle anyway(it'll be close enough), you should learn what DOPE is, and keep it.

[ExtremeX]

OP… I used a set of calipers as a ruler but the end results was the same…

You should do an experiment for yourself so you can better understand the difference.

You can introduce a measurement error using some mix/max values and see how it effects your drop tables for the load you are working with.

For example if you have a 1.5” height over bore, use a measurement of 1.25” and 1.75” and see the difference a gross error does to the tables.

You might be pleasantly surprised to know that close enough might just be good enough.

[2shotjoe]

take some calipers, measure the barrel where the end of the scope is, (a). measure the scope end, (b). measure the distance between the end of the scope to the barrel, (c).

((A+B=X)/2)+C=

[Webologist]

take some calipers, measure the barrel where the end of the scope is, (a). measure the scope end, (b). measure the distance between the end of the scope to the barrel, (c).

((A+B=X)/2)+C=

Nice, this is the most straightforward and accurate method yet.

[JMP]

You could do it the simple way(just using a ruler or some calipers and eyeballing it). Or you could do it the "I like to claim I have OCD and want to overthink everything and do it the difficult way), which doesn't require 2 people. It does require a dowel, something long enough to measure with, and an understanding of the pythagorean theorem.

Using a dowel to fit into the end of the bore(use wood or something), find the center point, run a line back to the center of the scope, this will be "C". Then run another line from the point you started with on the dowel and stop at a point where you can meet the end of "C" on the scope with a 90 degree angle, this will be "B". "A" is now the short line between the ends of "B" and "C". By the time you've finished reading this, and realized you can solve for "A", you could have just eyeballed it a half dozen times and been close enough, and probably wasted half an hour trying to measure that.

Instead of worrying about trying to get that measurement to be exact for a ballistic calculator that will not actually be exact for your rifle anyway(it'll be close enough), you should learn what DOPE is, and keep it.

If you take the time to do the down method, you should also use a piece of paper and run the down up to the eyepiece. You fold the paper down slowly while you are looking through the scope. When you have reached the axis of he scope, you can see through the scope clearly. This gives you the exact height as not all scopes simply have the axis down the middle.

Personally, I just estimate the bore height and adjust it so that it is correct on my ballistic calculator.

[sammass]

Hey Folks, thanks for the suggestions. Probably will cobble a bit from each.

Merc: I HAVE been accused of overthinking projects before. Since I usually like to do things only once, it tends to fall into the over thought OCD syndrome.

Sleighter: Leaving out details on the front end of a generic question muddies things. I have a Swiss K31 that essentially has a full Mannlicher stock. The objective bell is adjacent to the chamber & rear sight, difficult to centerline. Perhaps a wag is sufficient.

Merc: It has been a while since playing with 3-4-5 Right Triangles. :-) But as far as learning the Data On Personal Equipment, that was the object of the question. The K31 & scope setup is new to me. IF we consider the parameters needed to place a bullet on target and the BC asks for scope height in mm's so it can spit out a reasonable trajectory, I was only trying to give it the best info I could. Seems it wants reasonably precise data rather than have a GIGO result. With options for 527 reticles, 1737 cartridges, & 1184 bullets in the database, it goes a bit more that spit cleaning the front bead & Kentucky windage. The downfall to all the technical data requested is the sparse reference information provided. Have you a reference suggestion for bootstrapping myself up to speed on ballistics to make the calculations easier? Thanks.

Bloodhawke: Field stripped the K31 and still can't get to the barrel itself. Lumpy receiver & sight in the way. I'll bring the K31 & calipers to the meeting next month. Might be an interesting S&T. Thanks for the formula. :-)

Appreciate the suggestions to a newbie question. Be Well.

[Merc1138]

As mentioned already about the scope height, eyeball it. It'll be close enough. Obviously GIGO is bad, but if you play around with whatever ballistic calculator you're using, and look at the results if you change the scope height a little up or down, you'll see that it's not critical.

You have to remember that a ballistic calculator isn't going to give you a real world answer(technically they could, but you'd have to feed it a ton of data, and even that's not going to be 100%, and at that point we're talking about NASA level stuff trying to land on the moon and what not).

I don't know what calc you're using(some of the apps present things really poorly, or don't explain anything). Check this out http://www.jbmballistics.com/cgi-bin...j_simp-5.1.cgi it's simple enough to just plug in the data, and like ExtremeX said, change the values around for something like sight height and see if it really makes enough of a difference for you to worry about getting it accurate to the millimeter.

These calcs are useful tools for knowing what your cartridge should theoritically be doing. But you'll still need actual data to know what your cartridge is really doing. For example, velocities listed by manufacturers for ammo may be different than what you actually get out of your rifle(so get/borrow a chronograph). The atmospheric conditions(weather, altitude, etc.) are also going to affect the performance. Using a calculator isn't really DOPE(it kind of is I guess?), knowing what your equipment actually does under what conditions is DOPE.

I would suggest you start reading: http://www.calguns.net/calgunforum/s...d.php?t=295218

If you're the type that prefers video...

https://www.youtube.com/watch?v=pwG-D0HjCBQ&list=PLJUaiRIEduNXoal2_PkBZi0vDCIcEPxUn

Parts 25-33, parts 58-80, and possibly a few more. I'll warn you in advance though. He repeats things a lot(between videos that is, I don't mean nutnfancy levels of rambling). Some of that stuff is also way overkill(and you'll start to understand things that are missing from ballistic calcs, or why they're simply not relevant or an estimation will suffice).

[ExtremeX]

If you're the type that prefers video...

https://www.youtube.com/watch?v=pwG-D0HjCBQ&list=PLJUaiRIEduNXoal2_PkBZi0vDCIcEPxUn

Parts 25-33, parts 58-80, and possibly a few more. I'll warn you in advance though. He repeats things a lot(between videos that is, I don't mean nutnfancy levels of rambling). Some of that stuff is also way overkill(and you'll start to understand things that are missing from ballistic calcs, or why they're simply not relevant or an estimation will suffice).

[JMP]

Merc, because the bullet starts out of the rifle as a pretty straight line, you can get the bore height pretty close with your Kestrel. If you have a perfect zero with your rifle, back in the target to 25 yards and shoot. Adjust your bore height on your Kestrel until it gives you the 25 yard dope. This does a pretty good job interpolating from 0-100 yards. Bore height isn't a concern if you are shooting only well past your zero.

[sammass]

Ya know... sometimes it is better to be blithely ignorant. :-)

Merc et al: Thanks for the helpful words & references. I see I'm going back to college again. If I show up to the range bald and babbling, at least I'm making the attempt. :-) Video is good. The Rainov gear is impressive, but probably a bit overkill for taking out steel critters. JBM's data is staggering.

The calc is StrelokPro app for my iPhone & you are correct, the 'manual' is very sparse. A fellow shooter was using it to sort out my rifle, & I was smitten. 'course, he doesn't have fat fingers. I'll start with the basics with numbers I know and an educated guess on other stuff.

Y'all be well.