Why does this work? (front sight in front of scope)

divil · September 22, 2017, 05:39 PM

I'm putting a scope on my AR-15 and I thought the front sight post would get in the way with the low mounts I got with the scope. I read in various places that it doesn't really matter - so I tried mounting it and lo and behold - I seem to be able to see perfectly through the scope, even though the front sight post comes up most of the way towards the top! (See attached images).

Why does this work? Why doesn't the front sight post block the view? And, does it reduce the brightness of the image? Would I be better off getting taller mounts or should I just go with this?

Thanks!

Sharkbite · September 22, 2017, 05:53 PM

Go with it...

On lower magnifications the front sight will be visible. Either as a blurry shadow or more clearly as mag lowers towards 1ish.

If it doesnt bother you thru your magnification range, use it

James K · September 22, 2017, 06:32 PM

The front sight is there, but is so closeup and out of focus in the scope that it is in effect invisible.

Jim

krunchnik · September 22, 2017, 06:44 PM

Also-sometimes when mounting with higher rings it's more difficult to get a good cheek weld.

mavracer · September 22, 2017, 06:54 PM

https://en.m.wikipedia.org/wiki/Exit_pupil

FrankenMauser · September 22, 2017, 10:26 PM

Want to have some fun?
After testing, chop the sight to see if performance changes.

I had an upper with a standard FSB, and a 2-7x scope.
That front sight seemed to cause strange distortion, or at least 'distraction' with my eye. I couldn't actually "see" the sight above about 2.5x, but my brain knew there was something wrong with the sight picture through the scope. And the upper was not doing too well on paper.

After I chopped the FSB and made it a 'lo-pro' pinned gas block, groups closed by an average of about 1.75" at 100 yards.
Could have been the brain. Could have been the eye. Could have been a harmonics change for the barrel.
What ever it was, it worked.

jmr40 · September 23, 2017, 09:35 AM

On magnifications above about 3X the scope won't focus on it. Go with lower magnifications and you'll see it. On 1X it is perfectly clear, but I don't understand why some guys complain about it blocking the view. It doesn't obstruct the view any more than it would if using iron sights.

briandg · September 23, 2017, 10:23 AM

As Jim said, it is there. You have the large intake lens that will be taking in a large amount of light from all around the lens and then it's manipulated by other lenses and focused out downrange, then observed through an eight mm or so pupil. The sight sort of gets lost. You should be able to see it if you look carefully, as a blurry patch.

T. O'Heir · September 23, 2017, 11:40 AM

"...close up and out of focus..." Optics are just magical. snicker.
A higher mount will put the scope too high so your eye won't be in the right place.

rickyrick · September 23, 2017, 02:34 PM

I expected that the setup would look something like Franenmauser's, but when I looked at the OP's pictures I thought that that scope is mounted mighty low. It's important to fit everything to the shooter, but that setup looks uncomfortable for an AR.

I noticed that when you have an A2 sight post, light can reflect into the scope and be annoying.

Here's the ideal height for me, basically the cross hair is exactly the same position as iron sights would be.
Not saying yours is wrong for you, it'd be unnatural for me.

tangolima · September 23, 2017, 03:01 PM

Quote:

Originally Posted by rickyrick

I expected that the setup would look something like Franenmauser's, but when I looked at the OP's pictures I thought that that scope is mounted mighty low. It's important to fit everything to the shooter, but that setup looks uncomfortable for an AR.

I noticed that when you have an A2 sight post, light can reflect into the scope and be annoying.

Here's the ideal height for me, basically the cross hair is exactly the same position as iron sights would be.
Not saying yours is wrong for you, it'd be unnatural for me.

I agree. It is indeed too low. The scope's axis is below the top of the front sight post by 1/4” perhaps. It should be around the same height.

-TL

Sent from my SM-G930T using Tapatalk

divil · September 23, 2017, 06:02 PM

Thanks! It does feel a little low for comfort (it's lower than the irons as noted). It's not too bad though, I can see through it no problem.

BTW it's a fixed power 10x so no worries about lower zoom levels. I'll see if I can find mounting rings a little higher at a reasonable price, or else I'll just go with it as it is. I don't intend to leave it on this rifle for long anyway.

DaleA · September 24, 2017, 03:16 AM

Disclaimer: I don’t use scopes much and am nowheres near being any kind of expert on optical sights.

I’m sure there are books about scopes and mounting them, I just haven’t run across them. That’s kind of a hint if anybody knows of a good book on the topic.

Mounting the scope higher does lead to some ‘problems’ if you’re shooting at different ranges and especially if the ranges are short, like 25 yards to 100 yards. A friend sighted his AR in at 25 yards at his indoor range and found his rounds were hitting about a foot high at 50 yards. Note that the change isn’t nearly as much if the scope is mounted closer to the bore axis. This is pretty basic stuff that most shooters here already know but I’m mentioning it anyway.

One thing he was happy about was that he bought a one piece scope mount. He didn't have to mess with aligning the two rings of a two piece mount system. What he was NOT happy about was that he didn’t get a quick release mount. He’s got flip up iron sights on his AR. With the quick detachable mounts he can put the scope on and take it off without removing the iron sights. So if for some reason the scope failed he could just remove it and pop up the rear iron sight.

Here’s a nice Nikon one piece scope mount but it is NOT quick release:
https://www.midwayusa.com/product/37...op-ar-15-matte

Here’s a Burris once piece scope mount that IS quick release.
https://www.midwayusa.com/product/15...op-ar-15-matte

precision_shooter · September 24, 2017, 02:30 PM

Has to do with the magnification of the scope and the focal length or the distance in which images come into focus. I have a 1.25-4 power scope on my CZ 527 carbine with open sights. The front sight is nowhere near as tall as that on an AR, but I can see the front sight through the scope at anything less than 2.5x. It does not obstruct the reticle and only exists in the bottom 1/4 of the image.

Anything above 2.5x power, the image comes into focus beyond the end of the barrel so the front sight "disappears". Rather the image is zoomed past it.

bman940 · September 25, 2017, 09:55 AM

Obviously AR's and bolt guns are different in the scope height needed for a proper cheek weld. For the most part bolt guns run 1.25 +- and AR's 2.25 +- from mid bore to mid scope. I am not sure why you would have such a huge discrepancy with shooting from 25 to 50 yards though. Sighting in at 25 for a 100 yard zero you would want the POI to be roughly .75 inches low with a .223, 55 gr bullet at 3240 fps. By the time the bullet gets to 50 yards it should be about .27 inches low not a foot high. Something is definitely wrong. I go back and start at the base of the scope and work my way up.

I have also found that once you get past 2X on a scope the front post disappears. I have never found it to block my sight picture.

divil · September 25, 2017, 10:00 AM

Thanks for all the info everyone. I ended up ordering this one piece mount from Midwest Industries: https://www.midwestindustriesinc.com...i-sm30-blk.htm

It puts the scope at 1.5" above the rail, which is a bit higher than it is with these current mounts, which should make it more comfortable.

The mystery for me about the front sight post was just that it seems illogical. If there's an opaque object between my eye and the scene I'm looking at, then surely there must be some part of that scene from which light can't reach my eye? But obviously things are a bit more complicated that I thought lol!

September 22, 2017, 06:44 PM	#4
krunchnik Senior Member Join Date: October 27, 2010 Location: Lakeland,TN Posts: 220	Also-sometimes when mounting with higher rings it's more difficult to get a good cheek weld. __________________ THE CROW

September 22, 2017, 10:26 PM	#6
FrankenMauser Senior Member Join Date: August 25, 2008 Location: In the valley above the plain Posts: 13,424	Want to have some fun? After testing, chop the sight to see if performance changes. I had an upper with a standard FSB, and a 2-7x scope. That front sight seemed to cause strange distortion, or at least 'distraction' with my eye. I couldn't actually "see" the sight above about 2.5x, but my brain knew there was something wrong with the sight picture through the scope. And the upper was not doing too well on paper. After I chopped the FSB and made it a 'lo-pro' pinned gas block, groups closed by an average of about 1.75" at 100 yards. Could have been the brain. Could have been the eye. Could have been a harmonics change for the barrel. What ever it was, it worked. __________________ Don't even try it. It's even worse than the internet would lead you to believe.

September 23, 2017, 09:35 AM	#7
jmr40 Senior Member Join Date: June 15, 2008 Location: Georgia Posts: 10,806	On magnifications above about 3X the scope won't focus on it. Go with lower magnifications and you'll see it. On 1X it is perfectly clear, but I don't understand why some guys complain about it blocking the view. It doesn't obstruct the view any more than it would if using iron sights. __________________ "If you're still doing things the same way you were doing them 10 years ago, you're doing it wrong" Winston Churchill

September 23, 2017, 10:23 AM	#8
briandg Senior Member Join Date: May 4, 2010 Posts: 5,468	As Jim said, it is there. You have the large intake lens that will be taking in a large amount of light from all around the lens and then it's manipulated by other lenses and focused out downrange, then observed through an eight mm or so pupil. The sight sort of gets lost. You should be able to see it if you look carefully, as a blurry patch. __________________ None.

September 23, 2017, 11:40 AM	#9
T. O'Heir Senior Member Join Date: February 13, 2002 Location: Canada Posts: 12,453	"...close up and out of focus..." Optics are just magical. snicker. A higher mount will put the scope too high so your eye won't be in the right place. __________________ Spelling and grammar count!

September 22, 2017, 05:53 PM	#2
Sharkbite Senior Member Join Date: November 4, 2013 Location: Western slope of Colorado Posts: 3,679	Go with it... On lower magnifications the front sight will be visible. Either as a blurry shadow or more clearly as mag lowers towards 1ish. If it doesnt bother you thru your magnification range, use it

September 22, 2017, 06:32 PM	#3
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	The front sight is there, but is so closeup and out of focus in the scope that it is in effect invisible. Jim

September 23, 2017, 02:34 PM	#10
rickyrick Senior Member Join Date: March 15, 2010 Posts: 8,236	Why does this work? (front sight in front of scope) I expected that the setup would look something like Franenmauser's, but when I looked at the OP's pictures I thought that that scope is mounted mighty low. It's important to fit everything to the shooter, but that setup looks uncomfortable for an AR. I noticed that when you have an A2 sight post, light can reflect into the scope and be annoying. Here's the ideal height for me, basically the cross hair is exactly the same position as iron sights would be. Not saying yours is wrong for you, it'd be unnatural for me. Last edited by rickyrick; September 23, 2017 at 02:42 PM.

September 23, 2017, 06:02 PM	#12
divil Senior Member Join Date: November 11, 2009 Posts: 506	Thanks! It does feel a little low for comfort (it's lower than the irons as noted). It's not too bad though, I can see through it no problem. BTW it's a fixed power 10x so no worries about lower zoom levels. I'll see if I can find mounting rings a little higher at a reasonable price, or else I'll just go with it as it is. I don't intend to leave it on this rifle for long anyway.

September 24, 2017, 03:16 AM	#13
DaleA Senior Member Join Date: September 12, 2002 Location: Twin Cities, MN Posts: 5,312	Disclaimer: I don’t use scopes much and am nowheres near being any kind of expert on optical sights. I’m sure there are books about scopes and mounting them, I just haven’t run across them. That’s kind of a hint if anybody knows of a good book on the topic. Mounting the scope higher does lead to some ‘problems’ if you’re shooting at different ranges and especially if the ranges are short, like 25 yards to 100 yards. A friend sighted his AR in at 25 yards at his indoor range and found his rounds were hitting about a foot high at 50 yards. Note that the change isn’t nearly as much if the scope is mounted closer to the bore axis. This is pretty basic stuff that most shooters here already know but I’m mentioning it anyway. One thing he was happy about was that he bought a one piece scope mount. He didn't have to mess with aligning the two rings of a two piece mount system. What he was NOT happy about was that he didn’t get a quick release mount. He’s got flip up iron sights on his AR. With the quick detachable mounts he can put the scope on and take it off without removing the iron sights. So if for some reason the scope failed he could just remove it and pop up the rear iron sight. Here’s a nice Nikon one piece scope mount but it is NOT quick release: https://www.midwayusa.com/product/37...op-ar-15-matte Here’s a Burris once piece scope mount that IS quick release. https://www.midwayusa.com/product/15...op-ar-15-matte

September 24, 2017, 02:30 PM	#14
precision_shooter Senior Member Join Date: September 8, 2007 Location: DFW, Texas Posts: 2,475	Has to do with the magnification of the scope and the focal length or the distance in which images come into focus. I have a 1.25-4 power scope on my CZ 527 carbine with open sights. The front sight is nowhere near as tall as that on an AR, but I can see the front sight through the scope at anything less than 2.5x. It does not obstruct the reticle and only exists in the bottom 1/4 of the image. Anything above 2.5x power, the image comes into focus beyond the end of the barrel so the front sight "disappears". Rather the image is zoomed past it. __________________ "Laws that forbid the carrying of arms...disarm only those who are neither inclined nor determined to commit crimes...Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than to prevent homicides, for an unarmed man may be attacked with greater confidence than an armed man." - Thomas Jefferson, 1776

September 25, 2017, 09:55 AM	#15
bman940 Senior Member Join Date: August 29, 2010 Location: N. Texas Posts: 170	scope Obviously AR's and bolt guns are different in the scope height needed for a proper cheek weld. For the most part bolt guns run 1.25 +- and AR's 2.25 +- from mid bore to mid scope. I am not sure why you would have such a huge discrepancy with shooting from 25 to 50 yards though. Sighting in at 25 for a 100 yard zero you would want the POI to be roughly .75 inches low with a .223, 55 gr bullet at 3240 fps. By the time the bullet gets to 50 yards it should be about .27 inches low not a foot high. Something is definitely wrong. I go back and start at the base of the scope and work my way up. I have also found that once you get past 2X on a scope the front post disappears. I have never found it to block my sight picture. Last edited by bman940; September 25, 2017 at 10:08 AM.

September 25, 2017, 10:00 AM	#16
divil Senior Member Join Date: November 11, 2009 Posts: 506	Thanks for all the info everyone. I ended up ordering this one piece mount from Midwest Industries: https://www.midwestindustriesinc.com...i-sm30-blk.htm It puts the scope at 1.5" above the rail, which is a bit higher than it is with these current mounts, which should make it more comfortable. The mystery for me about the front sight post was just that it seems illogical. If there's an opaque object between my eye and the scene I'm looking at, then surely there must be some part of that scene from which light can't reach my eye? But obviously things are a bit more complicated that I thought lol!