Hi,
  I am about to place my order for the 2005 SEBR and have been looking at getting a few things for it but am a bit confused on the sight and optic options.

I don't have a lot of experience with AR's, I've only fired one once about 6 months ago and before that it was an M16A2 while I was doing my summer with the USMC during my youngster year at the Naval Academy.  

I'd like to get a BUIS until I can get an optic (have to be after christmas) but I am wondering if I need to get a rear and front sight or if the front sight the rifle comes with will work with the BUIS?

Also once I have an optic will the front sight interfere with the optic?  If so is it hard to remove the front sight.

I think I would prefer to remove the front sight anyway and put a buis in its place, but I don't know how difficult that is.

any advice appreciated.

OK, first issue.

If your rifle has a fixed front sight base (the standard sight on AR's, which I believe it will)....no problem. A BUIS should work perfectly fine with either, provided that you do not have a riser or something like that on your flattop. This would raise the height of a rear BUIS and would make zeroing almost impossible unless your rear sight is a special low model...but that is a whole other mess. If your flattop is bare, or just the flattop with nothing on it, you're OK. So the rifle as is, with a BUIS is good to go.

I recommend the Troy BUIS.


Second Issue:

"interfere" is kind of subjective. There are many ways people mount optics to a rifle. It also depends on what optic you are trying to mount.

If you mount an aimpoint for example, then the front sight base will certainly get in the way of your field of view. How much is the question. If you look at the sticky's at the top of this forum, there is a diagram of how this looks through a sight.

Seeing the FSB through the optic is a GOOD thing for most people (so long as the optic is not magnified).  This is called co-witnessing, and its purpose is to allow you to deploy or use your back up iron sights in the event your optic fails. There are 2 styles of co-witnessing. There is "absolute" or "center" co-witness. This is where your iron-sights line up dead center in the optics view. Then there is "lower 1/3" co-witness, this is where the iron-sights line up in the lower one-third of your optics view.

Obviously, the lower 1/3 style of co-witness keeps the front sight post and irons out of the way as much as possible to preserve the most field of view.


So, if you decide you want co-witnessing, you will have to pick a mount for your optic that achieves the desired co-witness. EOtechs are the same, they require a riser mount to co-witness in the lower 1/3. Aimpoints have a variety of mounts, and you'll have to find out how where each one mounts in height.


Now, if you don't want to see any iron sights in your field of view, then you will need to have both FLIP UP iron sights for the front and rear. Rear is no problem, as many of them come this way, and you just mount it to your flattop. The front ones are different. That will require you to remove the standard front sight base (which is also the gas block) and replace it with a gas block/flip up front sight combination base. The other option, would be to replace the FSB, and replace it with a gasblock that has picatinny railing on the top and possibly the sides (for other purposes) then you can add a detachable flip up front sight to this.


My advice. Forget messing with the front sight. Leave it be. In a scenario where you will have to deploy iron sights in the event your optic fails will be one where TIME is not on your side, therefore....having to deploy 2 flip ups vs. just the rear is a big increase in time. Rear BUIS that flip up are very fast. Much quicker to do that and stay in a shooting stance. Flipping up the front will take you out of your ready position.

Also, if you use the Aimpoint, then you can use the Aimpoint as a giant ghost ring with the front sight if you do not have time to even engage the rear flip up.


I prefer the rear flip up BUIS with a lower 1/3 co-witnessing mount for my optic. This is the best of all worlds. No front sight to mess with. The sights are reasonably "out of the way" of my field of view, and I still maintain co-witnessing capabilities. Oh, and the price is right. Front flip ups will add quite a bit to the budget, enough so that you can easily pay for a mount that does lower 1/3.


Beyond that, it depends on the individual optic you will choose. That will dictate which mount you want for what type of co-witness.


ALL of this is assuming the optic is not magnified. If you get an ACOG, or some other scope-type magnified optic, then the whole BUIS system must be thought out differently. For example, the magnified optic will probably need a quick detach mount so that it can be removed so that irons can work.......etc...

I'll concure with Dont-Tread-On-Me.

Get the Troy Rear BUIS, keep the fixed front sight, and the FSB is not a problem when using optics.

What type of optic are you planning on getting for this rifle?

No matter what optic you get the FSB will not interfere with your ability to get hits or see the target.  You will not gain any extra FOV by removing it no matter what optic you are using 1X or magnified.

Quoted: What type of optic are you planning on getting for this rifle?

I'm still trying to sort through all the threads on the different optics.

I'm leaning towards an acog but price will probably make me go with an aimpoint.  

If I do go the acog route (ta31f most likely) then would I need to get rid of the FSB?

Quoted: If I do go the acog route (ta31f most likely) then would I need to get rid of the FSB?

One more time, NO!

Quoted: No matter what optic you get the FSB will not interfere with your ability to get hits or see the target.  You will not gain any extra FOV by removing it no matter what optic you are using 1X or magnified.

aah good to hear

so right now looks like a rear buis and later on either an acog (ouch on the price) or an aimpoint.

Quoted: Quoted: If I do go the acog route (ta31f most likely) then would I need to get rid of the FSB? One more time, NO!

yeah read that after I had posted

I think I misunderstood Dont-Tread-On-Me's comment below and it confused me.

Quoted: ALL of this is assuming the optic is not magnified. If you get an ACOG, or some other scope-type magnified optic, then the whole BUIS system must be thought out differently. For example, the magnified optic will probably need a quick detach mount so that it can be removed so that irons can work.......etc...

thanks for all the help, this stuff is confusing when you try to take it all in at once.