Explanation of Co-Witness

[Tim_W]

I am building a 12" SBR. I am having trouble deciding on fixed or flip up BUIS for Co witnessing in the lower 1/3 of the sight picture. The optic will be a EO-Tech 553 or M3 with 4 moa dot. I have just read Pat Rogers latest article on red dot optics their proper uses in the Gun Rag and it has put me on the fence on this. I understand the negatives of having fixed centered Co witness site that was already out. What would you consider the best choice of the two, fixed 1/3 co witness or flip up centered or 1/3 co witnessed.

If going fixed it would be a LaRue rear BUIS with a standard pinned FSB or for the flips a set of Troy flip BUIS. This will be for a CQB and defensive gun, also the one I will use in classes such as Pats. It will be run hard by your definition Pat. It will be dirty far more than it will ever be clean. It will only be used with a zero magnification optic such as the two listed.

Which would give me the the best results in reliability and performance? Have any found a decrease in acquisition performance and speed with the fixed lower 1/3 co wit sites because of partial loss of that part of the site picture?

Do you know if the LaRue BUIS and FSB will Co wit to the lower 1/3 on the Aim point and the EO-Tech? Can they be made to with the proper LaRue mount? If so which. If it matters the hand guard will be a DD 9.5" FSB to a LaRue Upper.

Pat if you could weight in on this also I would appreciate your insight. By the way I tried to send you and IM on this question and it kicked it back because you're box is over full just an FYI.

Thank you in advance for taking the time to help.

Tim

ETA: I have tried sights both ways and they both seem to work well for me. I would give the edge to the fixed in transition speed. But I just don't know if others have found any deficiencies for having them fixed in the sight picture even if in the lower 1/3.

[Robb Jensen]

The rear sight height is the same regardless of which BUIS you have. The co-witness height is regulated by the optic and or mount. A 553 will co-witness in the lower 1/3. A 552 will if you use a LaRue EOTech mount.

[Tim_W]

What about the M3? Any preference to which you prefer fixed or flip in your goto gun.

Tim

[Robb Jensen]

What about the M3? Any preference to which you prefer fixed or flip in your goto gun.

Tim

Personally I prefer fixed rear sights like the LaRue or LMT. For a lower 1/3 co-witness for an M3 either get the LaRue LT150 mount a ADM AD-68H.

[Tim_W]

Thank you for the information. I am leaning towards the fixed at this point. Moving parts I think are just one more thing that can/will break or stop working when its needed.

Tim

[11B101ABN]

It was drilled into my exceedingly thick skull to have your flip-up BUIS deployed when engaging anyway, so I got rid of it and got the LMt fixed rear.

Never looked back. Your rear sight should be available for immediate use, always.

[Blake]

Tim_W,

This is a very user specific type of question. If you are able try both out extensively then make a choice. If you like both, then either make a choice or switch. I don't think anyone here can make a decision on something you need to make for your purposes. With that being said, you mentioned that it would be used in a defensive situation. Home Defense? Are you LE or MIL? You also stated that you would shoot it a lot. Is this for work or pleasure. The point is if you are going to shoot it a lot for training, and you would somehow manage to break of a flip up rear, you are immediately aware of it, you can fix it or replace it. If you are using it operationally then that is another story, breaking it would be of a big concern. If you are using it in home defense you're chances of breaking it are less of a concern. Not impossible. Neither choice is wrong, just a preference. Think about your needs in the most realistic sense.

[Chessbay]

So, I just got my Troy flip up BUIS in the mail today.

I have a cheap BSA Red Dot Scope mounted on my weapon right now as well.

Unfortunatley, I can't kick out for a better optic right now so I would like to make do with what I have for now if possible.

As it's mounted my optic is too low to have a true cowitness. The BUIS are almost looking over the top of the optic. They are at least in the upper third of the optic.

Is there a scope mount that I can use to fix this? Some type of shim?

Or am I SOL until I purchase a new optic.



Thanks for the help.

[Chessbay]

I've also noticed that my gas block sits about 1/4" lower than the flattop. This seems like it could create problems. Maybe not????

Man, I hate being completley new to something. I guess that's what site's like this are for.

Also, please correct me if I use the wrong terminology.


I've taken some pictures I'll try and post in the am.

[Shihan]

You would have to use a riser of some type. If you are planning on getting another optic in the near future I would just leave it as is and not waste the money.