Help with M4 Carbine set up please.

[Spear Dane]

Building my first flat top. Not sure of a few things which basically boil down to: What do I need to get in order for optic and irons to co-witness and at absolute or 1/3? What sling adaptor is on the stock? Mine did not come with one.

 

[JollyMon]

You need a lower third or absolute mount for your optic.

I dont understand what you are asking about in your second question. Is that what you want to build or is that what you have. What do you not have? The metal sling mount or the slot in the plastic....

 

[Spear Dane]

The slot is there. No mount. Looked all kinds of adaptors and didn't see one that looked right.

 

[Spear Dane]

You need a lower third or absolute mount for your optic.

I dont understand what you are asking about in your second question. Is that what you want to build or is that what you have. What do you not have? The metal sling mount or the slot in the plastic....

But which is better in terms of usability. 1/3 or absolute? Seems to me 1/3 because absolute would be having the dot or reticle directly on the FSP?

 

[BiscuitsandGravy]

I probably have a generic stock similar to the pic above with sling loop if you need one. Or just the sling loop...

 

[Ggreen]

I prefer absolute most of the time. I like the lower cheek weld. Lower 1/3 makes me feel like a giraffe. Counterpoint, I like lower 1/3 on my steel challenge /uspsa pcc's, it feels faster from draw to sight picture on that first target or after moving. Both have merits and I've seen no definitive edge one way or the other.

What stock do you have? A lot are coming with qd attachments now rather than the old loops.

 

[rhino]

I would skip trying to mount your sling at the tail end of the butt stock. Get a loop or other attachment point that mounts at the base of the receiver around the buffer tube. Then for not much money, you could get a Burnsed loops to attach near the front of the handguard.

I prefer absolute cowitness of red dot and irons.

 

[Hop]

If that picture in the OP is really what you have then:
-the slot is for feeding through a GI style strap and cinching it down using a buckle. Not real common. Some Carbine instructors like slings attached back there (Larry Vickers for one).
-the metal loop at the base of the buttstock is for a GI style sling with a clip. Like the slings seen on the M1 Garand. Fairly common.

You could swap out your lower's latch plate and install one with a sling mount or QD or loop. There's a ton of those out there. I stake my latch plates though, so swapping them isn't easy. I'm partial to QD attachments and place them all over the rifle.
I've used this with good luck. Midwest Industries adapter: https://www.midwestindustriesinc.com/product-p/mctar-30.htm

Co-witness or lower 1/3rd??? That's a can or worms. It depends on what optic, what magnification, fixed or flip up sights, etc...
I have a fixed front sight post AR with a fixed 4x ACOG. I can see the blurry front sight through the optic. That doesn't bother me. It does bother a lot of other people.
I have red dots set to 100% co-witness but only on guns with flip up front sights. Long range hits using an rds require a hold over. Can't see your target if there's a fixed sight post in the way. Flip down the sight or use a 1/3 co-witness. Pick your poison.