Line of sight in relation to trajectory.
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Old 01-11-2010, 07:03 PM   #1
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Default Line of sight in relation to trajectory.

I was always told; the closer your line of sight is to your barrel, the better. Can anybody tell me at what point you are compromising this theory by using a 50mm objective lens over a smaller objective lens? Is distance you are shooting a determining factor? Is versatility reduced by a larger scope. Is there a happy medium or is this whole idea flawed? If not, is it unadvisable to shim mounts to attain the closest possible distance from scope to barrel?

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Old 01-11-2010, 07:18 PM   #2
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I don't know if I either don't understand the question as you are asking it, or if I flat out don't agree with what you have been told.

Any distance rifle that we build, has a slanted scope mount. These are scope mounts that have MOA built into them, so you do not have to rack your scope knobs all the way up or all the way down, depending on distance.

Having said that, the front of the scope is going to be closer to the bore line of sight than the back of the scope is, right from the get go.

As such you would not be sharing the same line of sight, even if you could put the scope even with the bore.

This is where your ZERO comes into play. If your weapon has a scope that is 2 feet over the bore, but you are zero'd at 200 yards, you should be shooting dimes at 200 yards. Now, this is a gross exaggeration for purpose, no one is mounting a scope that far out of whack, but you should get the idea.

The angle of the scope, in relation to where your round will be, at time of impact, is what is going to determine how well you shoot at that distance.

If you take this axiom one step further, and are not shooting known distances, it IS going to be consistantly easier to handle "Kentucky Windage" or "SWAG" shooting than if your scope is at some super ackward angle or deviation.

Using a 50mm scope is not going to be a problem as long as you get good, quality rings and a good solid base to mount it on.

Once you do that, you zero the rifle for where you want to be shooting, write up a dope card, and you are field ready.

Hope that helps.

JD

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Old 01-11-2010, 07:19 PM   #3
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Just like with iron sights. The longer the sight radius (Distance between the front and rear sight) make a firearm more accurate. so does mounting a scope. The lower to the bore the less room for error (or so I have been told. The most accurate way would be to look threw the bore as you fired, but as far as I know there is no such thing as see threw brass and copper. There is however transparent alum.

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Old 01-11-2010, 09:35 PM   #4
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I ran some #'s on Line of sight. I picked 7mm Rem mag for this.
150 yard zero, 150gr Swift a-frame, 3110fps.
1.6" line of sight: .3" at 100 yards, 0 at 150, -1.5 at 200 yards.
2.5" line of sight: .1 at 100, 0 at 150, -1.1 at 200 yards.
3.5": -.2 at 100, 0 at 150, -.8 at 200.
4": -.4 at 100, 0 at 150, -.7 at 200

250 yard zero, 150gr Swift, 3110fps
1.6": 2.4" at 150, 0 at 250, -3" at 300
2.5": 2" at 150, 0 at 250, -2.8" at 300
3.5": 1.7" @ 150, 0 @ 250, -2.6 @ 300
4": 1.5 @ 150, 0 @ 250, -2.4 @ 300 yards.

I did the same w/ 55gr .223 and got similar results. I also have been told the closer the scope to the bore the better. Not so sure now.
If you look at the trajectory on a balistics calculater it see saws for lack of a better term at closer ranges. I never thought to use it to find the optimum scope size for a specific caliber. Very cool, great subject!!! I learned something from this that I would have sworn to be wrong before.

Edit, I used the Norma ammo public calculator for this test.

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Old 01-11-2010, 10:41 PM   #5
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Default line of sight

I spend about 4-6 hours a day in this forum and pretty much have learned who knows what they are talking about, who doesn't and who is full of B.S.. If I were to pick who replyed to my thread, It would have been the three of you who have already done so. THANKS MUCH !!

Although there some countradictions in your replys, it seems that they are all reasonable and true. It seems to me from those replys I can assume the higher a scope is mounted the farther apart the points the bullet crosses the line of sight would be and mid range trajectory would be farther above the line of sight. Also it seems as though having the gun straight up and down would be more critical because the angle between the LOS and bullet trajectory would be more acute. ???? Just a thought most people don't consider.

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Old 01-12-2010, 12:08 AM   #6
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Having everyting level makes a rather big difference in long range shooting it can make a difference in distances under 500 but 500+ you have some cant and boy oh boy your gonna see it on that big ole target down range. That is why you will see Palma and F-class guys using levels on their barrels, scopes and whatnot.

I doubt your going to see much of a difference in normal every day shooting with a scope that is 1.4" to 2.5" above the line of the bore.

I wouldn't worry to much about that. What I would worry about is this, how well your head is positioned on the stock and how stable it is. I have seen guys that mount a scope with a 50mm objective on it and they are shooting with their chin just touching the stock. that is not anywhere near a good steady cheek weld that you should have. 1.5" is about the average measurement from your cheek to your eye so that is why it is the most referred to measurement. There are some scopes with 72mm objectives not sure why but they are out there. Now that there is one hoonkin big azz objective. If I was wanting to do night hunting and didn't want to drop $10 K on a night vision scope that Zeiss would be the one I would get.

Zeiss 6-24x72 Victory Diavari 34mm Rifle Scope

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Old 01-12-2010, 12:23 AM   #7
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dteed - I think you are basically correct, but I think this "problem" boils down to this question:

How accurate is "accurate" for what you are trying to do?

Because, as Tango has indicated, shooting 1,000yard "F" class is going to be different from shooting groundhogs at 300 or 500 yards.

CAN'T in either your rifle or your scope, or both, is going to cause MUCH more havoc on you and your targets over the difference of 1" or 2" scope height above the bore.

For example, when we mount ANY scope, whether it's a $100 scope or a $3000 one, we have a right angle piece of 90 degree plastic that slips into the bolt rails of the action. On the perpendicular piece, we have a dead nuts center line that runs up the middle of the plastic.

When you have the scope mounted in it's rings, but before you tighten it down, you look backwards through the scope ( with it on the lowest possible setting ) and align the verticle axis of the scope exactly over the top of the line in the plastic. This aligns the scope 90 degrees to the bolt rails. Then you tighten the scope down and make sure it doesn't change.

This alone can make a MAJOR difference in groups where rifles' scopes had been mounted by eyesight.

I don't think, unless you are trying to shoot dime size groups at 800 yards or greater distances, that you are going to really see a drastic difference in a scope height choice if you do your part.

When all else fails, contact the maker of your scope, explain your application, and see what they say.

Good luck!

JD

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Old 01-12-2010, 12:46 AM   #8
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Tango, I've seen the "cast" shooting glove, bore levels and such on the firing line. I do agree that proper cheek wield is critical. I did this test on 7mm Rem Mag because it is my long range hunter. I have target rifles, but the same principals don't apply as they are set for specific distances or a set of distances. Hunting can be from 20 yards to 450 yards. I picked a 2-10x38mm Weaver for the task. It gives me 0..450 yards. Set w/ a 250 yard zero it does give me a 0..300 yard kill zone w/ 140.. 160gr loads. Quality of the glass is also a major factor. I do believe that the reason the variable scope was introduced was because cheaper/ inferior glass was used. I have a few German Military scopes that are 4x and incredable at light gathering. The
Ajack 4x90 is a great example of a true quality optic. You can see the reticule in complete darkness.

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Old 01-12-2010, 01:21 AM   #9
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Default No problem

I really am not having a a problem with Line of sight but thought it may be educational and answer a few questions which may not be relavent in what shooting I do. but it also stands to reason that understanding in depth the not so simple principles of balistics could help. I also think it is an interesting discussion with relatively knowledgeable people. I come here to discuss interests that most in this forum, to one degree or another share with me.

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Old 01-12-2010, 02:12 AM   #10
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Good topic.

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