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Posted: 8/30/2013 2:04:41 PM EDT
I have several recent build AR15s that I would like to accuracy test.  I have a scope that I use for load development, and I'm going to put it in a DNZ Reaper mount.  The ARs have different barrels, and are configured differently in terms of rails etc.  But the uppers are identical.  I don't want to have to bore sight each upper and spend a few rounds zero'ing them -- I'd like to zero one upper, shoot it, and then move the scope to the next upper (the lower will stay the same throughout the test, so cheek weld and position will be the same, along with fire controls, etc) and repeat.  

Of course I realize my zero won't be 100% on, but I'm going for group size and muzzle velocity data.  As long as I can hit a 8x11 sheet of paper at 100y so I can print the groups, I'm fine with it.

So the question is, assuming geometry on the upper receivers' rails is the same, can I expect a scope that is shared across a couple of uppers for an afternoon of testing to be able to produce hits that are "close enough?"

Link Posted: 8/30/2013 2:11:25 PM EDT
would be a large amount of luck involved in that, even slight differences in barrel alignment or the squareness of the receiver rail and can put you off a good bit rifle to rifle.  I have had it work out for me on a couple guns though.
Link Posted: 8/30/2013 2:14:03 PM EDT
DO NOT start at 100 yards!

Start at 25, or even closer until you see what is going on.

You might find that 50 works well, too.
Link Posted: 8/30/2013 2:19:30 PM EDT
Too many variables, even scopes on QD mounts removed and reattached to the same spot rarely retain zero.
Link Posted: 8/30/2013 2:27:33 PM EDT
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Quoted:
Too many variables, even scopes on QD mounts removed and reattached to the same spot rarely retain zero.
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My Larue and ADM do
Link Posted: 8/30/2013 2:40:37 PM EDT
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Quoted:
DO NOT start at 100 yards!

Start at 25, or even closer until you see what is going on.

You might find that 50 works well, too.
View Quote



This was going to be my response.
Link Posted: 8/30/2013 2:49:27 PM EDT
Cool.  Thanks guys.
Link Posted: 8/30/2013 3:08:25 PM EDT
Quoted:
I have several recent build AR15s that I would like to accuracy test.  I have a scope that I use for load development, and I'm going to put it in a DNZ Reaper mount.  The ARs have different barrels, and are configured differently in terms of rails etc.  But the uppers are identical.  I don't want to have to bore sight each upper and spend a few rounds zero'ing them -- I'd like to zero one upper, shoot it, and then move the scope to the next upper (the lower will stay the same throughout the test, so cheek weld and position will be the same, along with fire controls, etc) and repeat.  

Of course I realize my zero won't be 100% on, but I'm going for group size and muzzle velocity data.  As long as I can hit a 8x11 sheet of paper at 100y so I can print the groups, I'm fine with it.

So the question is, assuming geometry on the upper receivers' rails is the same, can I expect a scope that is shared across a couple of uppers for an afternoon of testing to be able to produce hits that are "close enough?"

View Quote



No.

I just did this.  TINY differences in rails/barrels/assemblies mean BIG differences in POI.  I moved the same scope between 4 uppers, just like you are talking.  Some of them were within 6 inches.  One was 18" different POI.
Link Posted: 8/30/2013 3:11:41 PM EDT
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Quoted:
Too many variables, even scopes on QD mounts removed and reattached to the same spot rarely retain zero.
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I then re-attached the original optics (ACOG in a LaRue, Aimpoint in a LaRue, Burris TAC30 in a LaRue, Leuopold 6.5x20 in a LaRue).  The WORST of them required 1 MOA adjustment.  That means all of them were within 1" at 100yds.  One was 1/2 MOA off, the other two were dead on.  That degree of difference can be attributed simply to the ammo brand I was shooting that day.
Link Posted: 8/30/2013 4:56:58 PM EDT
If it is a problem, you can always get a bigger sheet of paper.

Good data FALARAK.
Link Posted: 8/30/2013 5:01:28 PM EDT
It will be off from gun to gun. For example I have 2 AR's and the rear buis on one is adjusted to the left to get me on target and the other is adjusted towards the right to get me on target.
Link Posted: 8/30/2013 5:49:22 PM EDT
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Quoted:



No.

I just did this.  TINY differences in rails/barrels/assemblies mean BIG differences in POI.  I moved the same scope between 4 uppers, just like you are talking.  Some of them were within 6 inches.  One was 18" different POI.
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Quoted:
Quoted:
I have several recent build AR15s that I would like to accuracy test.  I have a scope that I use for load development, and I'm going to put it in a DNZ Reaper mount.  The ARs have different barrels, and are configured differently in terms of rails etc.  But the uppers are identical.  I don't want to have to bore sight each upper and spend a few rounds zero'ing them -- I'd like to zero one upper, shoot it, and then move the scope to the next upper (the lower will stay the same throughout the test, so cheek weld and position will be the same, along with fire controls, etc) and repeat.  

Of course I realize my zero won't be 100% on, but I'm going for group size and muzzle velocity data.  As long as I can hit a 8x11 sheet of paper at 100y so I can print the groups, I'm fine with it.

So the question is, assuming geometry on the upper receivers' rails is the same, can I expect a scope that is shared across a couple of uppers for an afternoon of testing to be able to produce hits that are "close enough?"




No.

I just did this.  TINY differences in rails/barrels/assemblies mean BIG differences in POI.  I moved the same scope between 4 uppers, just like you are talking.  Some of them were within 6 inches.  One was 18" different POI.


And when you think about it, if something is off in alignment by 1/10th of a degree, that equals 6MOA, so with all the parts that would need to be manufactured/assembled almost identically, it's not realistic to expect to be able to switch between rifles and have a relatively close POI.
Link Posted: 8/30/2013 5:58:58 PM EDT
Its so easy to bore sight just remove the bolt carrier and charging handle before you put the upper on the lower and put it in sandbags look down the barrel and adjust

your scope to the center of the target that the barrel is aimed at.  It only takes a few seconds for me to do it at 100 yards and I am usually less than 4" off.  That will be

a whole lot more accurate than just switching the scope with no adjustments.
Link Posted: 8/31/2013 3:38:15 PM EDT
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Quoted:
Too many variables, even scopes on QD mounts removed and reattached to the same spot rarely retain zero.
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Larue
Link Posted: 9/10/2013 5:27:17 PM EDT
simple solution is to just put your target on a large sheet of cardboard.

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