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Am I the only one that didnt know...

This is a discussion on Am I the only one that didnt know... within the Reference forums, part of the M14 M1A Forum category; that the rear sight windage hash marks on an M14 receiver were offset? When I got my Rock Ola rifle I hadn't noticed this until ...


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Old March 3rd, 2017, 03:44 PM   #1
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Am I the only one that didnt know...

that the rear sight windage hash marks on an M14 receiver were offset? When I got my Rock Ola rifle I hadn't noticed this until one day here on the forum in some other discussion it got me wondering and I looked at mine and its obvious they are offset to the right. So looking at my other M14/M1A rifles I see they are as well to a similar degree or other. I had asked JRA about this a while ago as if it were an issue, they didn't even respond and now I know why, not worth replying to my ignorance. From left to right is my TRW heel, Rock Ola, LRB and SAI. It can be seen that its about .75" from the left side to center of marks, but less than .75" to the right edge. I was thinking about this today when it dawned on me that my recently acquired TRW heel would be the final deciding answer. This may have been noted before but I didn't come up with anything on a search, and others need not feel compelled to find an earlier reference here.
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Old March 3rd, 2017, 03:54 PM   #2
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0.840 +/- .002" from left side wall (plane of the scope mount face).

However, if you measure carefully, you will find that the center graduation is within a thousandths of an inch, or two, on the bore centerline.
(The center of the threaded bore for the barrel is .842 - .003" for the same plane)

(If you are measuring from the edges of the "shelf" the graduations are on, these are not very tightly controlled features.)

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Last edited by lysander; March 3rd, 2017 at 04:22 PM.
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Old March 3rd, 2017, 03:56 PM   #3
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Old March 3rd, 2017, 04:20 PM   #4
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What is actually more interesting is that the graduations are not exactly centered between the "ears" of the sight well. You have about 0.004" more space to the right.

Just remember, the location of all features on a manufactured object are not equal. The more rigorously controlled the feature the more expensive it is to manufacture. The location of where the scope mount is, in relation to the bore centerline is very important, and therefore tightly controlled. Where the sides of the rear sight "ears" are in relation to the bore centerline is not, you cam move the rear sight side-to-side quite a bit, but the graduations should be close to bore center.

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Old March 3rd, 2017, 04:26 PM   #5
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I never noticed that
I have a receiver print from somewhere
, it is really a cluttered hard to decipher print but I'll give it a look

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Old March 3rd, 2017, 05:34 PM   #6
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Oh No, monfro...... I just notice that your heal engraving is also off center... Be thankful I sent back a Enterprise receiver that didn't have any windage scale.

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Old March 3rd, 2017, 07:34 PM   #7
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This was what made me really aware of this. My Rock Ola. It looks really off here but its not as bad when actually measured. I moved the front sight to compensate for some of this.
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Old March 3rd, 2017, 09:31 PM   #8
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You are correct - they are offset relative to the outside of the ears, but are centered relative to the bore, and relative to the sight deck.

THe rear sight shelf is not centered on the receiver because the receiver has the op-rod rail on the right side, so the right 'ear' is slightly thinner than the left ear.

Below are the drawings. As you see, the sight deck is 1.105 wide, so centerline is 0.5525 from the inside of the ear. The hash marks are centered at 0.840-0.2875= 0.5525. So these are the same and do line up with the bore.

However the elevation ear is fatter than the windage ear, so they are offset relative to the width of the back shelf.


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Old March 3rd, 2017, 10:07 PM   #9
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Quote:
Originally Posted by Phil McGrath View Post
Oh No, monfro...... I just notice that your heal engraving is also off center... Be thankful I sent back a Enterprise receiver that didn't have any windage scale.
Which one looks off? I just looked at them and all look centered.

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Old March 3rd, 2017, 11:32 PM   #10
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Quote:
Originally Posted by WaM14gunner View Post
Which one looks off? I just looked at them and all look centered.
Better take a second or third look again...........


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Old March 4th, 2017, 05:12 AM   #11
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That shooting sight fellow is pretty dang smart so I'll just agree with what he said .

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Old March 4th, 2017, 08:06 AM   #12
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Quote:
Originally Posted by ShootingSight View Post
You are correct - they are offset relative to the outside of the ears, but are centered relative to the bore, and relative to the sight deck.

THe rear sight shelf is not centered on the receiver because the receiver has the op-rod rail on the right side, so the right 'ear' is slightly thinner than the left ear.

Below are the drawings. As you see, the sight deck is 1.105 wide, so centerline is 0.5525 from the inside of the ear. The hash marks are centered at 0.840-0.2875= 0.5525. So these are the same and do line up with the bore.

However the elevation ear is fatter than the windage ear, so they are offset relative to the width of the back shelf.

Just a note...
The rear sight deck is 1.10 + .010", so the nominal width is 1.100" not 1.105".

And, the hash marks are 0.840 +/- .002", or 0.838" to 0.842"

So, the center graduation is nominally offset to the right by 0.002", and can be offset as much as 0.009".

Nominal ->

0.292 - 0.840 = .0548

and

1.10 / 2 = 0.550

Worst case ->

[0.292 - 0.009] - [0.840 + 0.002] = 0.559

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Old March 4th, 2017, 08:40 AM   #13
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Quote:
Originally Posted by Phil McGrath View Post
Better take a second or third look again...........
I did. Which one looks off to you?

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Old March 4th, 2017, 09:14 AM   #14
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The heel markings are centered between the left and right sides of the heel, but like ShootingSight noted, everything is shifted to the left because of the op-rod slot, the sides of the heel are not centered but shifted. However, the radius of the top curve of the heel IS centered on the boreline.

Note the drawing, a different section of the one Shooting posted:



The "V" created by the horizontal flat at the base of the rear sight will be centered on the "hump" of the heel, but the markings, centered between the left and right edges of the heel will not be centered on the "V". That's normal.

EDIT: when you look really closely at an M1 or M14 receiver they are very asymmetric.


(Note: this is a view from the bottom looking up, minus the internal details.)


Last edited by lysander; March 4th, 2017 at 09:34 AM.
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Old March 4th, 2017, 11:10 AM   #15
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Quote:
Originally Posted by Phil McGrath View Post
Oh No, monfro...... I just notice that your heal engraving is also off center... Be thankful I sent back a Enterprise receiver that didn't have any windage scale.
Quote:
Originally Posted by WaM14gunner View Post
Which one looks off? I just looked at them and all look centered.
Quote:
Originally Posted by Phil McGrath View Post
Better take a second or third look again...........
Quote:
Originally Posted by WaM14gunner View Post
I did. Which one looks off to you?
Just messing with you, April fool's came early......

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