This is my first post so excuse me if it is in the wrong section. My brother in law and myself are rookies concerning the ar 15. He purchased a new S&W M&P 15. It has flip up front and rear sights, along with a no name red dot sight. The red dot is right on at 35 yards. We were working on the front sight and ran out of light. Before this the front sight was shooting about 10 inches low. My brother says we must lower the front post to bring the sight picture up. Any advise is welcome.
Front sight Post down Brings the Pojectile impact up.
Why BZO at 35 yards?
That was the longest distance we had to work with that day.
https://www.m4carbine.net/showthread.php?t=7292
I found this very helpful. Apparently 50yds has about the same poi as 200m. I use a matech rear buis which has a 200m setting, then zero at 50yrds. Also if the red dot is right on, you could use that as a reference point for adjusting the irons.
yes try the 50 yard zero
The FSB has an arrow and ‘up’ marking; turning the sight as per the arrow (clockwise) will make the bullet strike point go up.
The sight has regular righthand thread, so tightening the sight makes it go lower on the sight base, raising the bullet strike.
Moon
Sorry for the hijack but I always sight in at 100. Not saying it is better and I read the last post about the improved BSZ but here is my ? If you zero at 50/200 what is the POI at 100?
the bsz goes like this…
dead center @50yards.
Dead center again @ 200meters
@125 yards it will be shooting high at about 1.5inches.-2inches
varies with your rifle barrel. so basically shooting at a man size target will result in a hit.
It depends on the barrel length and ammo. Take a look at the chart halfway down this page. You might find it helpful:
https://www.m4carbine.net/showthread.php?t=8585
Joe Mamma
basically it gives you the least deviation from your poi up to 200meters.
I just rezeroed my Gummint Carbine using the IBZ method at 50 yds, and it worked very well.
Here’s my question; with the large aperture A2 sight, hits are significantly low at 50 yds; in fact, my carbine has to be cranked to the 450 yd setting to bring the hits into the black. This is apparently pretty common.
Why should the short range aperture be so far off the POI for the smaller aperture? I like the large ghost ring, and it is quicker on target than the smaller one. But it is a pain to have to crank in adjustment when shifting from one sight to the other.
Moon
Because they are not on the same plane. The center of the large and small aperature on A2 iron sights or not at the same height.
if you have a standard a2 sights. you have to zero using the small aperture.
Have you ever wondered what 3/8 , 4/8 , 5/8 mean?
it means 300 yards, 400 yards and 500 yard zero. but there’s no marking for 200 yards right? you’ll have to adjust the allen on top of the A2 sights so you can drop the adjustment 2/8 . It doesn’t really show but just count the clicks. this is where you zero your 50yards.
using your small aperture, use 2/8 zero to shoot ibz. if you have a known target of 300 yards shift the sight to 3/8.
how to use large aperture. look at how it is marked.
“0-2” this means zero @200 yards. makes sense huh? Big and small aperture are not on the same plane. return your sights to 3/8.
If you’re shooting small aperture with 3/8 you’re zeroed to 300 yards. now use your large aperture with the sights controls STILL in 3/8. Now you have 200 yard zero.
Due respect, Warrior, but I had that part figured out. 
What I DON’T have figured out it why (as in ‘what were they thinking’) the closerange ap hits beaucoup low…I realize that there are replacement sights in the same plane, and I may make that change.
Were they thinking of center-mass hits at, say, 175 yds? Anyway, I use the long range ap to hit anything smaller than a breadbox.
Moon
Sorry if I sounded like an ass, I didn’t mean to.
Yea the A2 is a bit more work to IBZ but Lanceriley explained it pretty well for ya.
thanks warrior. it took me some time to understand how the ibsz works.
the marine 300 meter zero is itself the ibsz if you use the
0-2 large aperture.
it’s just a matter of moving the small aperture to the level of the large aperture for the ibsz. since we are civilian shooters who’s bent on showing off our ar’s accuracy:D
No problemo, Warrior. No offense taken.
Back to IBZ; If I understand it correctly, the rear sight is now bottomed two clicks up, but the relationship between the sight apertures remains the same.
One source actually said what I’ve been doing, and that is using the small ap for about anything.
Moon
yes that is correct. the relation ship of both apertures remain the same.
what I meant was that when you move the large aperture to 2/8. It is the same plane as the large aperture at 3/8.
you can basically use the small aperture in all of your shooting.
if you want to use the large aperture. set the dial to 3/8
Okay, LR, re- ‘splain that to me…
BTW, are you talking about a detachable carry handle? I’m dealing with A2 sights on a Gummint Carbine, and 8/3 is bottomed out, tho’ it is of course two clicks up.
I did add an XS sight white stripe front, and it is a help for old, blind farts like me.
Did get seven rounds into 1.1" at 50 yds (six into 0.9"); not too bad for an OBF with arns and green tip Lake City.
Moon
yes. im talking about your fix carry handle. there’s an allen on top of your sights that you can loosen to make it bottom out to 2/8