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E Pluribus Unum
09-30-2008, 12:28 PM
Well, I went out for opening weekend and I am having trouble sighting in my black rifles.

First rifle was my AR.

I have a flat top upper in an M4 configuration topped with tall rings supplied by Wes and a Bushnell 3-10x scope.

I started with left to right and got that close. I started 10 yards away from the target and shot until left to right was close. When I started to back up to get the elevation close my scope bottomed out. At 50 yards my POI was 4 inches low with my scope adjusted all the way. I assume it is because I had to use tall rings to get above that front site.

The second rifle was my Keltec. I lost the rear sight for it so I decided to through a BSA scope I had on it. I did the same thing, got windage adjusted by shooting close and working my way back. At 50 yards it was 2 inches low with the scope adjusted all of the way.

I tried to use a bore sighter but the extreme distance between the barrel and the scope meant it did not line up.

I thought about shimming one of the scope mounts but that might throw off the trajectory.


M1A's are so much easier.... :)

ohsmily
09-30-2008, 12:33 PM
Well, I went out for opening weekend and I am having trouble sighting in my black rifles.

First rifle was my AR.

I have a flat top upper in an M4 configuration topped with tall rings supplied by Wes and a Bushnell 3-10x scope.

I started with left to right and got that close. I started 10 yards away from the target and shot until left to right was close. When I started to back up to get the elevation close my scope bottomed out. At 50 yards my POI was 4 inches low with my scope adjusted all the way. I assume it is because I had to use tall rings to get above that front site.

The second rifle was my Keltec. I lost the rear sight for it so I decided to through a BSA scope I had on it. I did the same thing, got windage adjusted by shooting close and working my way back. At 50 yards it was 2 inches low with the scope adjusted all of the way.

I tried to use a bore sighter but the extreme distance between the barrel and the scope meant it did not line up.

I thought about shimming one of the scope mounts but that might throw off the trajectory.


M1A's are so much easier.... :)

Your scope doesn't have to be mounted "above the front sight" on your AR. Due to the effect of magnification and focus, the front sight won't even be visible in your field of view unless your scope is a 1 power or other lower power scope. How are you even going to get a proper cheek weld with the scope that high? Get some lower rings.

I have seen some crazy things lately with scopes. Make sure the turrets are oriented properly and you aren't using the windage as an elevation knob with the scope rotated 90 degree in the wrong direction.

The best thing for you to do is go to the range with someone who is experienced with sighting in optics. It usually takes me less than 5 rounds to get zeroed at 100 yards without using any special gadgets or gizmos (just visually sighting down the barrel and lining up the scope).

truthseeker
09-30-2008, 1:00 PM
If you don't have time to fix it before you go hunting, just hold 4 inches high on what ever you are shooting.

And before someone says "yeah, but that will depend on how far the target/deer is that he is shooting", I am assuming he is smart enough to figure that out on his own.

E Pluribus Unum
09-30-2008, 1:03 PM
Your scope doesn't have to be mounted "above the front sight" on your AR. Due to the effect of magnification and focus, the front sight won't even be visible in your field of view unless your scope is a 1 power or other lower power scope. How are you even going to get a proper cheek weld with the scope that high? Get some lower rings.


The rings I bought are about 2.5 inches high. It does not completely clear the front site but any lower ones would be obstructed. I bought them from 10% and Wes said he'd used them with success so I don't think it's that.


I have seen some crazy things lately with scopes. Make sure the turrets are oriented properly and you aren't using the windage as an elevation knob with the scope rotated 90 degree in the wrong direction.

I have them in the position I always have, the widage on the side, and the elevation on top.


The best thing for you to do is go to the range with someone who is experienced with sighting in optics. It usually takes me less than 5 rounds to get zeroed at 100 yards without using any special gadgets or gizmos (just visually sighting down the barrel and lining up the scope).

I am usually the same way. I have never been much of a black rifle fan. I have sited in scores of M1A rifles, .22 rifles, et cetera. I can also site in a rifle with limited shots but in this case the scopes just wont adjust. The only thing I can see different from the M1A is the distance between the scope and the barrel is much greater on my black rifles so I associated that with the scopes not adjusting.

Paratus et Vigilans
09-30-2008, 1:24 PM
At 50 yards my POI was 4 inches low with my scope adjusted all the way. I assume it is because I had to use tall rings to get above that front site.

At 50 yards, a .223 Rem. 55gr. round fired from a 16" 1/9 twist barrel should have a POI that is .73" below the POA, assuming you want a 100 yard zero AND the crosshairs of your scope are 2.5" above your bore. If you have rings that are 2.5" high, you probably have the crosshairs about 3" above the bore, so that extra half inch might account for some of the discrepancy, but certainly not all of it. You need to get out to 100 yards with a big enough target to get on paper, and see where you really are instead of where the ballistics charts say you ought to be.

E Pluribus Unum
09-30-2008, 2:19 PM
At 50 yards, a .223 Rem. 55gr. round fired from a 16" 1/9 twist barrel should have a POI that is .73" below the POA, assuming you want a 100 yard zero AND the crosshairs of your scope are 2.5" above your bore. If you have rings that are 2.5" high, you probably have the crosshairs about 3" above the bore, so that extra half inch might account for some of the discrepancy, but certainly not all of it. You need to get out to 100 yards with a big enough target to get on paper, and see where you really are instead of where the ballistics charts say you ought to be.

Thats weird. My M1A tends to shoot high at closer distances.

Paratus et Vigilans
09-30-2008, 2:51 PM
Thats weird. My M1A tends to shoot high at closer distances.


Different ballistics of the .308 vs. the .223. The 50 yard Improved Battlesight Zero (IBZ) for the M1A's .308 has the POI above the POA, while for the .223/5.56 of the M4 carbine it's below the POA.

The .223 has crossover points on its arc of flight at 25 yards and 300 yards and at 50 yards and 200 yards (the IBZ). (25 on the way up same as 300 on the way down; 50 on the way up same as 200 on the way down) The .308 is not the same in its arc, thus the difference. I don't know the .308 crossovers off the top of my head or I'd have put them here for comparison, but I do know that when I put the IBZ on my SOCOM 16 the 50 yard target for that had the POI above the POA.

E Pluribus Unum
09-30-2008, 3:06 PM
Different ballistics of the .308 vs. the .223. The 50 yard Improved Battlesight Zero (IBZ) for the M1A's .308 has the POI above the POA, while for the .223/5.56 of the M4 carbine it's below the POA.

The .223 has crossover points on its arc of flight at 25 yards and 300 yards and at 50 yards and 200 yards (the IBZ). (25 on the way up same as 300 on the way down; 50 on the way up same as 200 on the way down) The .308 is not the same in its arc, thus the difference. I don't know the .308 crossovers off the top of my head or I'd have put them here for comparison, but I do know that when I put the IBZ on my SOCOM 16 the 50 yard target for that had the POI above the POA.

well, that went way over my head. I'm on the phone now so I cannot research it. I will do so tonight.

I have always been under the impression that bullets rise out of the barrel, crest, and the come back down in a steady uniform curve, the angle of which determined by ballistic coefficient of the bullet and muzzle velocity. Apparently this is incorrect as it seems as if you are suggesting that the bullet rises and falls.

rksimple
09-30-2008, 3:12 PM
The rings I bought are about 2.5 inches high. It does not completely clear the front site but any lower ones would be obstructed.

2.5 inches to center line is pretty dang tall. While it may not be the root source of your issue, it could contribute to the problem. Once again, like ohsmily said, your front sight disappears at around 2.5-3x. No visual "obstruction" is present in the FOV.

rksimple
09-30-2008, 3:16 PM
well, that went way over my head. I'm on the phone now so I cannot research it. I will do so tonight.

I have always been under the impression that bullets rise out of the barrel, crest, and the come back down in a steady uniform curve, the angle of which determined by ballistic coefficient of the bullet and muzzle velocity. Apparently this is incorrect as it seems as if you are suggesting that the bullet rises and falls.

Not exactly a uniform curve as the bullet is going much slower on the latter half of its flight, but you have the right idea.

http://www.globalsecurity.org/military/library/policy/army/fm/23-10/Fig3-25.gif

CSACANNONEER
09-30-2008, 3:59 PM
To zero your scopes try this:

Don't waste your time with a laser boresighter.

http://www.calguns.net/calgunforum/s...ad.php?t=98980

You do have another problem. The rails on your Keltec are pliable and the rings will need to be tightened several times before they hold securely to the rail. When the SU16 first hit the market, there was an article in Dillon's Blue Press about how to properly mount optics to a SU16.

E Pluribus Unum
09-30-2008, 4:55 PM
Not exactly a uniform curve as the bullet is going much slower on the latter half of its flight, but you have the right idea.

http://www.globalsecurity.org/military/library/policy/army/fm/23-10/Fig3-25.gif

That is exactly how I understood it to be. If that is the case, how can a bullet hit 2" low at 50 yards but still be on target at 100 yards? That is a LOT of bullet travel.


Update:
Ok... I feel better... I am not a complete idiot...

I went down to the gun store and bought a $50 bore sighter. I plugged it on the Keltec and that thing is all over. The windage knob doesn't even change the POI and the elevation knob adjusts both windage AND elevation. It is a wonder I got the thing centered at all!

So... cheap $70 scope is bad; big surprise. I wasted 30 rounds of ammo on that POS. I hate being broke. :)

The bore sighter has also confirmed that I cannot adjust the scope on the AR. The bore sighter POI shows the exact place on the target I was hitting and I cannot adjust the scope any further. I will now use the bore sighter to mess with the rings and try to get it moved enough to allow for some adjustment.

Fjold
09-30-2008, 6:08 PM
Bullets never rise. Gravity always works.

The only reason that a bullet is above the line of sight is because the barrel is pointed up at an angle relative to the line of sight.
http://img.photobucket.com/albums/v214/Fjold/Boreline.jpg

E Pluribus Unum
09-30-2008, 6:43 PM
Bullets never rise. Gravity always works.

The only reason that a bullet is above the line of sight is because the barrel is pointed up at an angle relative to the line of sight.
http://img.photobucket.com/albums/v214/Fjold/Boreline.jpg

I do not think that is correct my friend. I thought because of aerodynamics a bullet will actually rise slightly when it leaves the barrel. At least that is what I have gathered from Ballistic charts issued by ammunition manufacturers.

aplinker
09-30-2008, 8:00 PM
I do not think that is correct my friend. I thought because of aerodynamics a bullet will actually rise slightly when it leaves the barrel. At least that is what I have gathered from Ballistic charts issued by ammunition manufacturers.

No. Bullets do not rise. There's no force that could do that with a bullet.

You could have done "bore sighting" with your AR by looking down the bore.

Move the elevation knob to the extreme down, then the extreme up. Count the number of clicks to go from one extreme to the other. Once you're at the extreme up, put it back in the middle.

Do the same (exchange up/down with left/right) with the windage.

Now, try adjusting your scope looking down the bore at something approx 50-100yds away.

Sometimes knobs need to be "worked" to work.

Fjold
09-30-2008, 8:07 PM
The sights are above the height of the barrel so therefore to make the bullet impact at the level of the sights at close range the barrel has to be tipped up.

The manufacturer's ballistics charts are usually based on the sights starting out 1.5 inches of the line of the bore.

Gravity always works as there is no way for a spinning object to generate lift in air.

Here's a real good explanation for it;
http://www.loadammo.com/Topics/October01.htm

aplinker
09-30-2008, 8:26 PM
The sights are above the height of the barrel so therefore to make the bullet impact at the level of the sights at close range the barrel has to be tipped up.

The manufacturer's ballistics charts are usually based on the sights starting out 1.5 inches of the line of the bore.

Gravity always works as there is no way for a spinning object to generate lift in air.

Here's a real good explanation for it;
http://www.loadammo.com/Topics/October01.htm

Just to clarify, no way for an object spinning perpendicular to its direction of travel to generate lift in air.

Airsoft uses spinning to compensate for drop.

E Pluribus Unum
10-01-2008, 12:17 AM
The sights are above the height of the barrel so therefore to make the bullet impact at the level of the sights at close range the barrel has to be tipped up.

The manufacturer's ballistics charts are usually based on the sights starting out 1.5 inches of the line of the bore.

Gravity always works as there is no way for a spinning object to generate lift in air.

Here's a real good explanation for it;
http://www.loadammo.com/Topics/October01.htm

I stand corrected. Thank you sir.

Maybe you can explain this to me:

My scope would not adjust far enough and even at the crosshair's highest adjustment, it was still 2 inches low. To correct this I decided to shim one of the rings. I theorized that if I raised the barrel so that it was on bulls-eye, the scope would be 2 inches above the bullseye. In order to correct this, I would need to shim the back ring to angle it downward. When I shimmed the back ring it made the problem worse. I then switched the shims to the front ring and voila, I was able to adjust the scope to bulls-eye.