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Pinger5.56 · Mar 27, 2014

I have a truglo red dot 30mm dual color optic and if I mount it on the rail the front iron sites on my sport are in the way, do I need a riser I have been asking around but with no straight answer yet on the what to use as a optic on this weapon and still be able to use the iron with the magpul flip up rear sites. Can anyone out there help. I have shot AR's in the past but this is my first owned one. Thanks to all that reply

sithlord · Mar 27, 2014

Sounds like you want lower 1/3 cowitness..

Use this riser:
Amazon.com: UTG High Profile Riser Mount with 3 slots: Sports & Outdoors@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41FRHfwAuKL.@@AMEPARAM@@41FRHfwAuKL

ChattanoogaPhil · Mar 27, 2014

For all those who find co-witness and risers puzzling.

Remember the 12in wooden or plastic ruler you were taught to use in kindergarten? Get one.

Measure from the rail to the tip of the front sight post or figure 1.4in (that will be close enough). Then decide about where you would like to see the tip of the front sight post in the glass of the optic. If it's the middle, then measure from the rail to the middle of the glass. The difference between the two measurements will tell you what riser height options you are looking for. Generic risers typically come in .25in increments. .5in .75in and 1in, so your measurements need not be micrometer exact. Typically you'll be choosing between .5 and .75 risers for dime store red dot tubes with built-in mounts.

Otherwise, get an optic and mount designed for an AR platform. They come in all price ranges so if you are buying new there's no advantage in struggling to piece together generic stuff. Suggest visiting Primary Arms web site. They sell a wide array of optics with matched AR platform specific mounts, and provide vids to help you understand and decide between absolute and lower 1/3 co-witness.

JaPes · Mar 27, 2014

ChattanoogaPhil said:
Otherwise, get an optic and mount designed for an AR platform. They come in all price ranges so if you are buying new there's no advantage in struggling to piece together generic stuff. Suggest visiting Primary Arms web site. They sell a wide array of optics with matched AR platform specific mounts, and provide vids to help you understand and decide between absolute and lower 1/3 co-witness.

Phil's entire post is a home-run. The last section is very sage advice for new people to the AR-15 rifle, and new to red dot optics. Most people are looking for an inexpensive dot of good quality. Primary Arms has built a reputation for providing affordable optics, good customer service, and good quality for the price.

I have had the pleasure of owning one, and shooting another.

Type I owned:

Primary Arms M3 Style Red Dot on a high cantilever mount.

This was during the time where I felt I had to put everything and the kitchen sink on a rifle. The high cantilever mount was so that I could push the optic forward on the limited flat top rail space and accommodate a rear flip up sight and eventually a PA 3X magnifier on a swing to side mount. I turned a nice light rifle into a top-heavy pig.

Type equipped on a rifle I shot a few times:

Primary Arms Micro Dot With QD riser combo.

For $99 + Shipping, the Microdot is the one I would choose.

WU_Who · Mar 27, 2014

If using a Tru-glo 30mm RDS, you'll want .5" riser to co-witness with your magpul flip ups. This is the set up I have on my 15-22.

Pinger5.56 · Mar 27, 2014

thanks

Thanks for the straight up answer, I spent most of the money on the rifle and love the flip up site and that classic iron in the front and did not want to remove either, I wanted to co witness with my Truglo Red dot 30mm dual color that I did pay like 70.00 bucks for and it says its for a shotgun. I did not like it on my shot gun but do like it on the AR-15 platform I have. So there is no difference in the 2 rifles yours being a .22 LR and mine being a 5.56. Do u have any idea to where to buy one of those .5" risers everywhere I look they are all to long need on like 3.25-3.5" long. Thanks again

ChattanoogaPhil · Mar 27, 2014

You should be able to find something here.

http://www.cheaperthandirt.com/prod/Picatinny_Rail_Riser

Pinger5.56 · Mar 27, 2014

sithlord said:
Sounds like you want lower 1/3 cowitness..

Use this riser:
Amazon.com: UTG High Profile Riser Mount with 3 slots: Sports & Outdoors

I would like to co-witness with my Truglo 30mm RD

cyphertext · Mar 27, 2014

Pinger5.56 said:
I would like to co-witness with my Truglo 30mm RD

Uh huh, we got that... but what type of co-witness? Absolute co-witness or lower 1/3 co-witness?

WU_Who said:
If using a Tru-glo 30mm RDS, you'll want .5" riser to co-witness with your magpul flip ups. This is the set up I have on my 15-22.

Does that give him absolute or lower 1/3 co-witness?

Pinger5.56 · Mar 27, 2014

Pinger5.56 said:
I would like to co-witness with my Truglo 30mm RD

absolute that is sorry

Pinger5.56 · Mar 27, 2014

sithlord said:
Sounds like you want lower 1/3 cowitness..

Use this riser:
Amazon.com: UTG High Profile Riser Mount with 3 slots: Sports & Outdoors

absolute that is sorry

cyphertext · Mar 27, 2014

Pinger5.56 said:
absolute that is sorry

Are you sure? If you think the front sight post is in the way, why would you want absolute? I'm guessing that you don't fully understand what that picture is showing. In the lower 1/3 pic, it is trying to illustrate that the user is looking over the top of the iron sights when using the red dot. To use the irons, he would lower his head to look through the irons. With absolute, the user is actually looking through the rear sight when using the red dot.

This is assuming you have fixed sights, or keep your sights up at all times. With the Sport and absolute co-witness, the front sight is going to go about half way up in the sight picture of the red dot. If you shoot with both eyes open, focusing down range on the target, this really doesn't matter as you will not notice the front sight.

I hope I am not coming off like I am picking on you. Just want you to understand the difference and be able to make the correct choice for you. I have two rifles with a fixed front sight post. I run my .22lr with absolute co-witness with fixed front and rear sights, and I run the Sport with lower 1/3 and keep the rear sight lowered. I don't notice the front sight on either rifle.

Pinger5.56 · Mar 27, 2014

Here is a pic of my truglo installed on the rifle without a riser mount
Yes the weapon is unloaded. maybe this will help with what I need for this red dot.

Pinger5.56 · Mar 27, 2014

cyphertext said:
Are you sure? If you think the front sight post is in the way, why would you want absolute? I'm guessing that you don't fully understand what that picture is showing. In the lower 1/3 pic, it is trying to illustrate that the user is looking over the top of the iron sights when using the red dot. To use the irons, he would lower his head to look through the irons. With absolute, the user is actually looking through the rear sight when using the red dot.

This is assuming you have fixed sights, or keep your sights up at all times. With the Sport and absolute co-witness, the front sight is going to go about half way up in the sight picture of the red dot. If you shoot with both eyes open, focusing down range on the target, this really doesn't matter as you will not notice the front sight.

I hope I am not coming off like I am picking on you. Just want you to understand the difference and be able to make the correct choice for you. I have two rifles with a fixed front sight post. I run my .22lr with absolute co-witness with fixed front and rear sights, and I run the Sport with lower 1/3 and keep the rear sight lowered. I don't notice the front sight on either rifle.

I know that you are not picking on me, I really like all the hints you are giving me, this is my first AR-15 platform rifle. I have owned my AK-47 platform rifles and shotguns. I am glad that this forum is here with you AR gods on it to guide me thanks to all. I have replaced the hand guard and the pistol grip with both Magpul products. I just would love to have that red dot being used cause I did pay like 70.00 for it and it looks better on the AR than the shotgun.

JaPes · Mar 27, 2014

ChattanoogaPhil said:
Measure from the rail to the tip of the front sight post or figure 1.4in (that will be close enough). Then decide about where you would like to see the tip of the front sight post in the glass of the optic. If it's the middle, then measure from the rail to the middle of the glass. The difference between the two measurements will tell you what riser height options you are looking for. Generic risers typically come in .25in increments. .5in .75in and 1in, so your measurements need not be micrometer exact. Typically you'll be choosing between .5 and .75 risers for dime store red dot tubes with built-in mounts.

^ Break out a ruler.

I'm eyeballing it but it looks like you might need a 1/2 inch riser. Don't hold me to it.

cyphertext · Mar 28, 2014

Ok, so from your pics, the red dot definitely sits too low. So, what you need to do is like Phil said... For absolute co-witness, pop your rear sight up and measure from the rail to the center of the peep sight. If memory serves, it should be 1.4" from the rail to the center of the aperture. Then measure from the rail to the center of the red dot lens. Subtract that from the measurement you took for the rear sight and you will know what size riser you need for absolute co-witness.

If you want lower 1/3, then you will need a higher riser. Same concept though, measure from the rail to where you would like to see the rear sight in the red dot sight picture. Subtract that from the measurement you took between the rail and rear sight.

That will give you the correct answer, and you understand how you arrived at it.

Pinger5.56 · Mar 28, 2014

JaPes said:
^ Break out a ruler.

I'm eyeballing it but it looks like you might need a 1/2 inch riser. Don't hold me to it.

That is what someone said a 1/2 riser would work. I have been trying to get a answer from truglo but that has not happened yet I need one that is 3.25-3.5" long to fit what flat top rail that is left in front of the magpul flip up site

JaPes · Mar 28, 2014

All you need is a riser long enough to accommodate your dot optic. Break out a ruler and measure the length of the base of your optic. Leave the rear folding sight mounted directly to the flat top rail.

Pinger5.56 · Mar 28, 2014

cyphertext said:
Ok, so from your pics, the red dot definitely sits too low. So, what you need to do is like Phil said... For absolute co-witness, pop your rear sight up and measure from the rail to the center of the peep sight. If memory serves, it should be 1.4" from the rail to the center of the aperture. Then measure from the rail to the center of the red dot lens. Subtract that from the measurement you took for the rear sight and you will know what size riser you need for absolute co-witness.

If you want lower 1/3, then you will need a higher riser. Same concept though, measure from the rail to where you would like to see the rear sight in the red dot sight picture. Subtract that from the measurement you took between the rail and rear sight.

That will give you the correct answer, and you understand how you arrived at it.

so it figures out to me for absolute co-witness I need a .5" riser for 1/3 co-witness I need a 1" riser that is what it measured out on my ruler.

Pinger5.56 · Mar 28, 2014

JaPes said:
All you need is a riser long enough to accommodate your dot optic. Break out a ruler and measure the length of the base of your optic. Leave the rear folding sight mounted directly to the flat top rail.

my red dot is 2.5 inches long

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