I cant believe that I cant figure out how to sight in my gun.   Let me give you guys some details.  I have a Flattop and just bought a new ARMS #40 rear BUIS, and also the replacement front sight that is taller than the standard. I was told that I would need both because the rear BUIS is taller than normal.   Anywho, I put the new front post in and screwed it down until the circular part of the post was flush with the front sight base.  

Now I hit the range and tried to zero at 50 yards.   All my shots right off the bat were low, about 2 inches low from the center of the target.  Since I am an idiot, I thought, oh maybe I should raise my front sight post up to fix that.  Nope didnt work, made it worse.   So I lowered it, and I still couldnt get the shots to hit the center of the target.   What am I missing here?  Also, why doesnt this rear BUIS have elevation?  Is that normal?  Do I just need to use the front sight post for elevation at this point?

Any help would be awesome, I apologize for being an idiot.......

Most BUIS don't have elevation.  As to your front post, screw it in ( clockwise) to raise your groups.

As you  already found out, any adjustment to the front sight has a reverse correllation.  If you want to lower your elevation, you have to raise the front sight and vice versa.  (The same holds true for windage. )

The ARMS 40L does not have any elevation adjustment.  LMT make a BUIS with both elevation and windage adjustment.  You need to use the front sight post for elevation adjustment.  Remember to adjust it in reverse.

Quoted: LMT make a BUIS with both elevation and windage adjustment.

The elevation adjustment on the LMT (and all other A2 style rear sights) is for bullet drop compensation, not for zeroing.

Quoted: You don't need a tall FSP. Zero with the original.

It had been recommended to me by Bushmaster as well as many others here in this forum.  Something about that ARMS#40 being designed for the Colt guns, and that thier sights are generally "taller" than other manufacturers.   Are you sure I didnt need the taller sight?

Quoted: You don't need a tall FSP. Zero with the original.

+1.  I have 2 Bushy carbines with ARMS #40s and I don't need a taller front sight post.

Quoted: Quoted: You don't need a tall FSP. Zero with the original. It had been recommended to me by Bushmaster as well as many others here in this forum.  Something about that ARMS#40 being designed for the Colt guns, and that thier sights are generally "taller" than other manufacturers.   Are you sure I didnt need the taller sight?

The stock sight post will "work" with a #40 rear sight but you have to raise it to the point of looking gay to zero for 50 yards.  I don't care about looks and my sights work so I'm not fixing what isn't broken with mine.

If you are still hitting low, lower the front sight post more.  It is the only method of elevation adjustment you have.  If you keep twisting and impact never gets higher maybe it's not threaded in right?  Also note... the "UP --->" marking you see on the front post base is not talking about the post, it's talking about bullet impact.  I got nailed by that my first time out.  If you turn in the direction of the "UP" arrow on the post you are lowering the post and raising the point of impact.

Quoted: The stock sight post will "work" with a #40 rear sight but you have to raise it to the point of looking gay to zero for 50 yards.  I don't care about looks and my sights work so I'm not fixing what isn't broken with mine.

Not neccissarily.

With my 2 carbines neither required much adjustment from factory 'zero'. (where the base of the sight is even with the flat part of the FSB).

There seems to be a wide variety of possible outcomes.  As the tall sight prevents zeroing it's obvious he needs the standard sight get zeroed.

Quoted: Also, why doesnt this rear BUIS have elevation?  Is that normal?

On standard A2 sights, the elevation knob is for distance changes, NOT for initial zeroing.  That is all done at the front sight.

Quoted: Quoted: The stock sight post will "work" with a #40 rear sight but you have to raise it to the point of looking gay to zero for 50 yards.  I don't care about looks and my sights work so I'm not fixing what isn't broken with mine. Not neccissarily. With my 2 carbines neither required much adjustment from factory 'zero'. (where the base of the sight is even with the flat part of the FSB). There seems to be a wide variety of possible outcomes.  As the tall sight prevents zeroing it's obvious he needs the standard sight get zeroed.

Interesting.... On my Bushy barrel the front post base is slightly above the level of the front sight base.  It looks a little odd, but like I said it works fine.  I'd agree, ditch the tall post and use a standard post instead.

Well now Im glad I asked.  I started another thread similar to this in the optics and sights forum and got an amazing response saying that I NEEDED to have this post.  I guess I should have tried to shoot with the old one first, before switching. I will switch it back and try again.  

Quoted: Quoted: Quoted: The stock sight post will "work" with a #40 rear sight but you have to raise it to the point of looking gay to zero for 50 yards.  I don't care about looks and my sights work so I'm not fixing what isn't broken with mine. Not neccissarily. With my 2 carbines neither required much adjustment from factory 'zero'. (where the base of the sight is even with the flat part of the FSB). There seems to be a wide variety of possible outcomes.  As the tall sight prevents zeroing it's obvious he needs the standard sight get zeroed. Interesting.... On my Bushy barrel the front post base is slightly above the level of the front sight base.  It looks a little odd, but like I said it works fine.  I'd agree, ditch the tall post and use a standard post instead.

Yeah, My Bushy's front sight post sticks up rather high also, it was the only way to get it to zero at 50 yards (standard 20" A2). I was seriously considering sending it back to bushmaster or ordering the tall front sight post since none of my other AR's require the front post to be this high.