Riser blocks for co-witness on M&P Sport

moonshine44 · Dec 24, 2011

There's a possibility that I may be getting a firearm of some sort as sort of a belated Christmas present this year, based on some things my wife has said lately. My choice is the M&P Sport, based on handling one at Cabela's a week ago and a lot of research on this and other sites.

If this does come to pass, I'm planning to install a red dot sight. I've been reading about "co-witness" of the sight, and I think I've got a pretty good handle on that idea. So here's my question: I will be using this rifle mostly as a coyote gun for use on calling stands. This is probably one of those "Your mileage may vary" things, but in the opinion of you fine folks, what is more useable for quick target acquisition with a red dot, absolute co-witness or 1/3 co-witness? Which riser blocks will I want to use for each? Amazon has UTG blocks of different heights for less than $10 each, so if I need to get one of each height I won't be out much money...

Thanks in advance, folks.

Merry Christmas!

JaPes · Dec 24, 2011

IMO, the minor difference in optic height between 1/3 co-witness & full co-witness is not the issue. I've tried it on my 15-22. The red dot will stand out either way.

What you need to decide is where you need the range of adjustment. Lower 1/3 co-witness will give you more upward adjustment of the red dot position, sacrificing downward adjustment. Full co-witness provides equal adjustment range for the red dot.

This is my M&P 15-Sport with a Primary Arms M3 red dot sight on a high cantilever mount. The mount height allows for a full co-witness. If I ever choose to add a magnifier, the cantilever mount makes it possible on the available rail space. I'd affix the red dot mount as far forward as possible, and add the magnifier behind it.

https://www.primaryarms.com/Primary_Arms_s/586.htm

WebSnyper · Dec 24, 2011

JaPes said:
IMO, the minor difference in optic height between 1/3 co-witness & full co-witness is not the issue. I've tried it on my 15-22. The red dot will stand out either way.

What you need to decide is where you need the range of adjustment. Lower 1/3 co-witness will give you more upward adjustment of the red dot position, sacrificing downward adjustment. Full co-witness provides equal adjustment range for the red dot.

This is my M&P 15-Sport with a Primary Arms M3 red dot sight on a high cantilever mount. The mount height allows for a full co-witness. If I ever choose to add a magnifier, the cantilever mount makes it possible on the available rail space. I'd affix the red dot mount as far forward as possible, and add the magnifier behind it.

https://www.primaryarms.com/Primary_Arms_s/586.htm

I thought the PA M3 and high cantilever mount provided lower 1/3...

Here's a link to the PA subforum on AR15.com that shows that same mount and sight picture, etc.

Whats the difference in Absolute co-witness and 1/3 co-witness - Page 1 - AR15.COM

I have that same mount and sight on my 15-22 MOE and thought it was lower 1/3. I'll have to check that again tomorrow.

JaPes · Dec 24, 2011

WebSnyper said:
I thought the PA M3 and high cantilever mount provided lower 1/3...

Here's a link to the PA subforum on AR15.com that shows that same mount and sight picture, etc.

Whats the difference in Absolute co-witness and 1/3 co-witness - Page 1 - AR15.COM

I have that same mount and sight on my 15-22 MOE and thought it was lower 1/3. I'll have to check that again tomorrow.

It's hard to get things lined up on a camera. When co-witnessed, my irons & dot line up in the middle of the scope.

Rear = Magpul MBUS
Front = A2 F Marked

I also have a 15-22 equipped with Magpul front & rear MBUS sights. I could swear the Magpul front MBUS is physically lower than an A2 post sight.

alumltd · Dec 31, 2011

Riser height

Hi JaPes,

What is the effective riser height of your mount above top of picatinny rail?

Is it .5", .83" or 1.0"?

I need riser for a SIG STS-081 Mini Red Dot Sight & have a single slot YHM .5" riser installed but need the RDS higher... just not sure if .83" is high enough for MBUS & A-2 front post for "Absolute Co-Witness".

Alex

meanmrmustard · Dec 31, 2011

A one inch riser, depending on the mount height of the optic, allows a lower 1/3. .83" is absolute.

alumltd · Feb 15, 2012

MeanMrMustard... many thanx for the riser height info.

I ended up with UTG's #RS08S2 .830" saddle height, 2-slot, medium profile riser mount for an "absolute co-witness".

1 thing was hoping for was its "thumb screw" quick detach capability. For ~$11.00, it's hard to beat.

TangoFoxtrot · Feb 19, 2012

My setup is MBUS rear, Truglo red dot, and A2 f mark front for absolute co-witness.It works well for me. If my eyes get worse I will need to add a magnifier.

maninblak · Feb 20, 2012

my eotech co-whitnessed mounted straight onto the receiver on my sport.

oneyeopn · Feb 20, 2012

My Ultradot cowitnessed absolutely mounted straight on my Sports receiver also, and it worked with the rear sight up or down!

danco · Feb 20, 2012

Personally, I like lower-1/3 cowitness, as the higher optic height (even 0.3-0.5 inch) makes for a faster target acquisition, without reqiring a perfect cheek weld. (I also prefer the larger window of EOTech holosights.)

~Dan

Riser blocks for co-witness on M&P Sport

moonshine44

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JaPes

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WebSnyper

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JaPes

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alumltd

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meanmrmustard

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alumltd

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TangoFoxtrot

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maninblak

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oneyeopn

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danco

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