Line of Sight - Line of Bore Qn.
 

OK, I'm having a brain cramp.

We know that the line of the bore must be angled upward (however slightly)in relation to the line of sight, in order for the bullet to hit the point of aim. We know that the bullet will cross the line of sight twice, once about 25 yds from the gun, and again some distance downrange. I get this part.

Here's the question. When shooting with a scope, where does thisangle come from? Scope mounts seem interchangeable front to back (or should be), so that's not it. Doesn't seem like guns are manufactured to provide this angle in the scope mounting area. So that leaves the scope itself. I can believe that, but I guess I don't know enough about how scopes work to understand it.

Can anyone explain how a scope provides this angle between the line of sight and the line of the bore, and how it can actually be adjusted to change the angle? When you adjust the crosshairs, are you actually adjusting the angle that the scope is "looking"? How is that achieved?

RE: Line of Sight - Line of Bore Qn.
 

It is just the difference in the height the scope is above the barrel. The only way to adjust it is having a lower or higher mounted scope. With see though bases that you can use the open sights with is a good example. The scope will be sitting much higher and the angle between the barrel and scope will be much more. This is also combined with the balistics of the load that you are shooting which creates the arced path of the bullet.

RE: Line of Sight - Line of Bore Qn.
 

Nope. That's not where the angle comes from. The scope could be two feet above the barrel, and the angle between the bore and the scope (adjusted toits optical center) would be the same. It would have a dramatic effect on the angle needed to sight in for a given distance though. I'm really asking how does adjusting the scope change that angle? What are the parts in the scope that are being moved?

RE: Line of Sight - Line of Bore Qn.
 

The angle you are referring to is the difference between the line of sight and the line of the bore. I've had trouble trying to explain this to the old timers who refused to believe that the bullet starts to drop the second it leave the bore. They were convinced that the bullet rises when it leaves the bore. And I told them that is because the bore is slightly pointed up just the way you described.
Now, from what I recall, the rifle scope has mirrors and prisms inside, when you adjust the scope you are actually rotating these mirrors. This is why your reticle is always centered. I believe the mirrors or prisms are held in place by opposing springs allowing for up/down, left/right adjustment. So to answer your question, the angle comes from inside the scope.
If sure if I am wrong, I will get jumped on.

RE: Line of Sight - Line of Bore Qn.
 

bronko22000
Consider your self it, high powered scopes like spotting scopes use mirrors and prisms for the most part normal rifle scopes are straight through,though there are a few targetor varmint rifle scopes that are an exception.
UncleNorby
If I understand your question correctly this is the answer.
scopes have a octagonal ring which is adjusted by the windage and elevation adjustments in which the cross hairs are mounted this moves the cross hairs around on the seen you see when you look through the scope. It actually works some thing like your back sight. Hope this helps. Lee

RE: Line of Sight - Line of Bore Qn.
 

You are saying exactly what I as thinking, just did not know if it was true. I never really gave it a lot of thought before. I guess I thought that the crosshairs were moving up/down and left/right with adjustments. Then I got thinking about it and that really did not make sense, or account for the angle issue.

Do others agree or know that the scope adjustments are actually rotating mirrors, lenses, or even prisms?

I'd really like to see a picture of the guts of a scope and how the adjustments work. Anybody know where I could find one?

RE: Line of Sight - Line of Bore Qn.
 

This from a website:

Mechanics
The inner workings of a scope have a direct affect on shooting accuracy. As adjustments are made during sight-in, the cam tube, which holds the reticle and lenses in place, moves inside the scope. To stay on target and produce a quality image, this tube must be strong enough to absorb the impact of heavy recoil during shooting and remain in place. When selecting your riflescope look for precision (positive) adjustments, point-of-impact consistency, reticle strength and waterproof, fogproof and shockproof durability. You'll also want to consider weight, bulk and ergonomics, which are especially important during long days in the field.

So there is this cam tube thing that moves inside the scope. If that's tru,I can see how it could be angled up and down or left/rightto varying degrees. Starting to make sense.

RE: Line of Sight - Line of Bore Qn.
 

http://www.shootingtimes.com/optics/meade_101705/index.html

RE: Line of Sight - Line of Bore Qn.
 

UncleNorby

New scopes certainly work that way - I still have to old weaver K4's that the cross hairs do move in.... seems really odd when you look throught the scope and the cross hairs are off in the corner....

Remember some of the arly Bausch and Lomb scope did not even have turrents - you had to buy adjustable rings...

RE: Line of Sight - Line of Bore Qn.
 

All great info. Thanks.

RE: Line of Sight - Line of Bore Qn.
 

I am not exactly sure what you guys mean by angle?? there is no inherent angle built into a scope to allow the line of sight to cross the trajectory twice.

A scope can easily be adjusted to only touch the line of trajectory once, or cross it twice.

First off the bullet never rises. The angle comes from two variables.

Lowering the scope to cross the trajectory-the same way you can raise it to be above the trajectory.

Mainly the angle comes from the fact that trajectory has an ever increasing trajectory curve. Or in other words the farther the bullet gets from the bore-the greater the "bullet drop". This additional drop is what causes the bullet to cross the "line of sight" at either a close distance with a slow cartridge or farther out with a faster cartridge.

IMO what got you thinking about this was the post you had on the Encore base being tilted downward because of the barrel taper(with the longer base). IMO that post was erroneousbecause the base is NOT pointed downward becuase of barrel taper. I think that guy just made that up. Tom.

RE: Line of Sight - Line of Bore Qn.
 

You're right, there's nothing built into a scope to create the angle. The angle needs to be adjustable to allow for different applications.

I disagree that a bullet can cross the line of sight only once. If it crosses once, it must cross again further downrange, assuming it doesn't hit anything of course.

True, bullets don't "rise", they only fall away from the line of the bore. That is the trajectory. But, in order for it to be possible for the bullet to hit the target, it must be fired at an upward angle in reltion to the liine of site. The line of the bore and the line of sight intersect at some distance downrange, say around 25-35 yds. That's why most people take a few shots at 25 yds when a new scope is installed. If you hit dead on at 25 yds, you're on the paper at 100.

Changing the heightof the scope in relation to the bore, say with low or high scope mounts, does change the angle that must exist between the line of bore and the line of sight, but not much.

RE: Line of Sight - Line of Bore Qn.
 

Notice I said "Touch the line" Not "Cross the line of sight only once". Tom.

RE: Line of Sight - Line of Bore Qn.
 

Really? The base is NOT pointed down? So you have examined that individual's gun, AND mine, and determined this? Or you are just the typical internet know-it-all who speaks authoritatively without any actual knowledge of the subject? So tell us...the scope is bad, the mount is bad, or the solution is always shooter error and you know this HOW? If a gun is shooting low, something is out of line, so by all means with no actual experience with the equipment involved do tell us how you work your magic from hundreds of miles away...

The truth is, you know nothing of the situation and are relying solely on assumptions. Assumptions with no basis in either fact or experience. When you actually own or have ever mounted a scope on one of the guns in question, come back and play. You "think" I made that up, just like you "think" you know everything about the mounting surface of TC guns without ever having worked with one.

Ever notice how you can crank the elevation on a scope from top to bottom and the reticle always appears the same? That is because it is. It is permanently etched, unchanging, on the internal glass. The horizontal crosshair never moved with relation to the vertical crosshair. This piece of glass is mounted inside an internal tube that move up or down, left or right, as you crank the turrets. When the tube hits the side of the turret, you run out of elevation or windage. This is why a 30mm tube has more adjustment than a 1inch tube. The scope can be then mounted parellel to the bore, yet you get the angle because of the angle between the INTERNAL tube and the barrel.

I think some people get confused when you say "the bullet never rises". It depends on your point of reference. If you say "the bullet never rises with reference to the line of the bore", you are correct. But if you are the shooter, the bullet indeed rises above your line of sight to the target because the bore will be angled up to account for the drop. Battleships arc shells a few miles in the air en route to target, so with relation to the ground they certainly rise. But they never rise above a line drawn straight out of the bore.

RE: Line of Sight - Line of Bore Qn.
 

Ha Spaniel: Shove it up your ***. Tom.

RE: Line of Sight - Line of Bore Qn.
 

Now, now, Spaniel. We like to play nice on this forum. You can make your point without being offensive. [:-]

RE: Line of Sight - Line of Bore Qn.
 

sheesh! Thedog needs a spanking.

RE: Line of Sight - Line of Bore Qn.
 

You can indeed adjust the scope so that the bullet only rises to the line of sight once. This is not reccommended because it limits your effective "aim, shoot and don't worry" zone. If you adjust so that the trajectory intersects the line of sight at 25 yds (approx) rises above and then falls back through the line at around 100 yds, you will be about 1 1/2 in high at 60 yds and 2 - 3 in low at 150 yd. If your hold is steady you have 150 yds of worry free shooting. If you adjust to only touch the line of sight once, that will be around 40 - 50 yds. by 100 yds yo will be 3-4 in low and at 150 6-8 in low. Your worry free zone is now only about 80 yds. After that the ball- bullet falls like a stone and you have to think and adjust your point of aim.

RE: Line of Sight - Line of Bore Qn.
 

I agree. Which is why when I am trying to help a fellow poster solve an issue with which I have experience and have fixed several times before, I do not appreciate the attitude and accusations of "making stuff up". It's fine to have differing opinions (I acknowledged the legitimacy of the multiple solutions suggested), but if you're going to outright accuse fellow members of making stuff up you'd better have more to go on than a few unsupported assumptions or expect something from it. And the cussing, such class. I know neither of us come here for this though so I'll leave it.

RE: Line of Sight - Line of Bore Qn.
 

Some bases are pointed down deliberately - I think rarely would you have one pointed up ;)(all with respect to line of bore). Picatinny rails can be had with varying minutes of offset for many bolt action and black rifles (well, really I don't care what color they are :D). It would be nice if there was such flexibility in buying bases for muzzleloaders. A common problem nowadays involves scopes running out of upward adjustment before 100 yard zero is reached with the bp gun. Leupolds tend to have limited adjustment ranges compared to several other brands and are often involved when such problems arise. Be nice if a guy could just determine what offset is needed to get a scope to its optical center, then order accordingly. Shimming sux.

But that would be far too much to ask of the gun industry. Nowadays one is lucky to get a rifle with iron sights that actually work well on the rifle.