Why do scopes not "see" the front fixed sight?

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arco59

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I tried searching for this but didn't find what I was looking for in the posts. I have a cheap 4-9x scope on my M4 and recently purchased a much nicer Mueller Speed Shot scope which is a 1-4x. I have not purchased mounting rings for it yet because Im not sure how high/low/forward I can place it without the front fixed sight being blocked or in the way of viewing the reticle.

So my question is this: In the picture is my current setup. I do not see the fixed sight in the optic. Can I assume the same will be true for the 1-4x? Im thinking not but I want to know why. Any resources on the subject of this would be appreciated. I have asked some friends and they basically say the same "Its weird but thats how they work" Thank you
 

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You don't see it with the 4-9x because of the depth of field of the focal length. You WILL see it with the 1-4x, at least until you get past 2x. I have a 1-4x on my AR and ended up replacing my front sight with a low profile gas block.
 
Not an optical engineer, but my understanding is that it's so close to the objective lens that it's so far out of focus that you can't see it. I have a Nikon P223 on one of my ARs and I can barely see a shadow at 3x.
 
Most scopes cannot focus close enough to see the sights. To check this scope look through it at 1x at objects about the distance you would be mounting the scope from the sights.
 
That is not how mine works. I have a 1.5-5x Bushnell on my RRA and I do see the front sight post in mine. Actually, the top of the front sight is centered in the scope crosshairs. It bothered me at first but I got used to it.

c379e620-86d0-434f-8a65-d03290f84c77_zps075fc2ab.jpg

I am only guessing but it might be that the higher powered scope doesn't focus on the front sight; so it is there but is so blurred that you don't see it, unlike in a lowered powered scope.
 
So let's say you were planning an AR build that was to include a scope---there's no need to eliminate the front sight by using a low-profile gas block instead of a combination front sight/gas block? Is there any advantage at all to the low profile block?
 
just because you can't see it, doesn't mean it's not affecting/limiting the light going into the optic. it's usable, but the image is less bright and you are losing some clarity


try this test. get comfy and look through the scope at a target. ask a friend to take a piece of cardboard and slide it 1/4 way across the objective from the top, and then halfway, and then 3/4, and watch the image. then try the same from the side. repeat at various magnifications
 
Thanks everyone and thanks for the link RCModel. I think I will have to buy scope mounts with 1.5" of height or so. I may get a low profile gas block to increase the field of view without obstructions at low power. HexHead can you point me in the direction of the raw parts I would need to do this? I want to avoid the hacksaw :D
 
Oh, don't do that!

1.40 inches is the height of the AR/M16 iron sights.

You don't want your scope mounted any higher then that in order to get a good stock cheek-weld when sighting through the scope.

rc
 
If I were building scoped only rifle, without a back-up sight, I'd consider shaving down the FSB and adding a free float rail.

I had to cut off the bayonet lug and sling mount on my 6920 to make room for a Centurion C4 rail and it was easy work with a Dremel cutting wheel, then the grinding attachment to clean it up.
 
A couple years back my brother had a friends Tikka. The scope went down to 2x and you could see the front sight. On 3x you could not see it.

On various rifles you cant "see" it but you can sometimes see the blur where it is.
 
I'm running a Trijicon TA33 (3x) and a faint shadow is visible at times buy if you position close to the optic, the front sight is not visible at all. Being more of a SHTF rifle, I want to keep the front sight with the flip up rear so no plans to change.
 
arco59 said:
. . . my M4 and recently purchased a much nicer Mueller Speed Shot scope which is a 1-4x. I have not purchased mounting rings for it yet because Im not sure how high/low/forward I can place it without the front fixed sight being blocked or in the way of viewing the reticle.
Click to expand...

arco59 said:
I think I will have to buy scope mounts with 1.5" of height or so.
Click to expand...

rcmodel said:
Oh, don't do that!

1.40 inches is the height of the AR/M16 iron sights.

You don't want your scope mounted any higher then that in order to get a good stock cheek-weld when sighting through the scope.
Click to expand...

Honest question here. Will raising the scope 0.10" matter much in this configuration of a 1-4x scope on a collapsible stocked carbine?

I mean, people choose lower co-witnessed sights/red dot combos frequently which raises the dot 7mm (0.276") above the sights. It would seem with a low power scope that coming up only 0.10" might not be such a big deal with a carbine in this configuration.
 
I have a 1-4x scope with a fixed FSB (carbine gas). It's not ideal for using the scope (see it at low power, goes away around 2x as mentioned above), but it's completely usable.

If it tickles your fancy, consider the recommendations for shaving down the FSB, installing a (longer) free float rail, and then perhaps putting a folding backup sight on top
 
chicharrones said:
Honest question here. Will raising the scope 0.10" matter much in this configuration of a 1-4x scope on a collapsible stocked carbine?

I mean, people choose lower co-witnessed sights/red dot combos frequently which raises the dot 7mm (0.276") above the sights. It would seem with a low power scope that coming up only 0.10" might not be such a big deal with a carbine in this configuration.
Click to expand...

Considering how the 0.4" high flat-top iron sight plane is already 0.2" or so higher than the A1/A2 sights, which were designed for optimal cheek weld for the average shooter; and how using a carbine stock will lower your head even further since you are resting your cheek on the buffer tube rather than on a stock that covers it like on an A1/A2, the irons on an AR carbine are already too high for a comfortable cheek weld... at least for an apparently average-sized shooter like me who has perfect cheek weld on an A1/A2.

Putting the scope even HIGHER than flat-top irons just makes the cheek weld issue that much worse. Unfortunately, pretty much every one-piece AR mount is over 1.4" high; most being 1.5" or higher. I am actually in the process of switching all my scoped ARs to an extended picatinny riser and regular rings, for this very reason.

As you point out, lots of people use a lower 1/3 co-witness with a red dot, where the sight is considerably higher than the irons. While I personally don't care for this setup, it isn't as much of an issue as with a scope because most red dots are virtually parallax-free, which means you can have your head down level with the irons and the bullet will still impact where the dot is. Also, most red-dot equipped ARs are set up more for close quarters, and with that style of shooting, cheek weld isn't as important as it is for more precision-oriented shooting. You don't need a super stable precision shooting position to put rounds in center mass at 21 feet. Lots of the other fundamentals of marksmanship are foregone in favor of speed and mobility with that style of shooting... which only makes sense.

But presumably if you're going too have a scope on your rifle, you anticipate a use that calls for a bit more precision than a pure CQB rig -- and having a solid cheek weld is an important part of the fundamentals of marksmanship.
 
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henschman said:
Considering how the 0.4" high flat-top iron sight plane is already 0.2" or so higher than the A1/A2 sights, which were designed for optimal cheek weld for the average shooter; and how using a carbine stock will lower your head even further since you are resting your cheek on the buffer tube rather than on a stock that covers it like on an A1/A2, the irons on an AR carbine are already too high for a comfortable cheek weld... at least for an apparently average-sized shooter like me who has perfect cheek weld on an A1/A2.

Putting the scope even HIGHER than flat-top irons just makes the cheek weld issue that much worse. Unfortunately, pretty much every one-piece AR mount is over 1.4" high; most being 1.5" or higher. I am actually in the process of switching all my scoped ARs to an extended picatinny riser and regular rings, for this very reason.

As you point out, lots of people use a lower 1/3 co-witness with a red dot, where the sight is considerably higher than the irons. While I personally don't care for this setup, it isn't as much of an issue as with a scope because most red dots are virtually parallax-free, which means you can have your head down level with the irons and the bullet will still impact where the dot is. Also, most red-dot equipped ARs are set up more for close quarters, and with that style of shooting, cheek weld isn't as important as it is for more precision-oriented shooting. You don't need a super stable precision shooting position to put rounds in center mass at 21 feet. Lots of the other fundamentals of marksmanship are foregone in favor of speed and mobility with that style of shooting... which only makes sense.

But presumably if you're going too have a scope on your rifle, you anticipate a use that calls for a bit more precision than a pure CQB rig -- and having a solid cheek weld is an important part of the fundamentals of marksmanship.
Click to expand...

I agree on many points. My interest is similar to arco59's (the OP's) interest. I have a 16" carbine that I recently pulled off the M4 stock and put on an A1 stock. So, I have tossed around the idea of pulling off the lower 1/3 co-witnessed red dot and scoping it.

Of course, the A1 stock offers to raise my cheek by about 0.13" over the "mil-spec" diameter buffer tube of my M4 stock.

I think the carbine "F" marked front sight base is only 0.040" higher than an A2 FSB, and from what I've seen that is just the shelf the post rides in and not the sight's "ears". It would seem then that if the ears aren't higher, then the overall height between a carbine FSB and a rifle FSB are essentially the same in regards to scope line of sight.

So, not just the 0.10" height increase of the scope mounts are a problem for cheek weld, the carbine stock adds another 0.13" or so to that 0.10". Just under 1/4" total in this situation. Like you mentioned above, compared in red.

Still, I wonder how bad that really is for a 1-4x scope that the OP has purchased which is really a variable power red dot? No reticle, no crosshairs, just a 4 MOA red dot that the shooter can zoom in as wanted. It might be favorably compared to a lower 1/3 red dot with a 3x magnifier behind it, just with less weight and less cost.

http://muelleroptics.com/mueller-speed-shot-1-4x24

http://muelleroptics.com/wp-content/uploads/2011/05/Speed-Shot-Actual-Photo-Use.jpg

https://www.youtube.com/watch?v=rvMfbYwED1k
 
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When I said the sights on the flat tops are higher than the A1/A2, I was referring to how the rear sight is about 0.2" higher on the flat top. Yes, they had to put a slightly taller FSB on the carbines so they could have enough adjustment to zero with the taller rear, but overall sight height is around 0.2" higher. They did this to accommodate the rear adjustable elevation mechanism so it could be adjusted out to 600m... gots to be able to shoot across the course at a high power match with your 14.5" carbine don't cha know!
 
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