Zeroing in new front and rear sights

dontcatchmany · September 12, 2010, 08:50 AM

I am getting a new M&P 15R which has no rear iron sight.

I am intending to put on the Magpul rear flip up sights and replacing the M&Ps original front sight with a Magpul front flip up....as well as a different gas block.

I will eventually put on optics that have a true cowitness(gosh I do not like that term) with the flip ups when needed. My initial goal is to thoroughly familiarize my self with and become competent in using the "iron" (actualy polymer) sights prior to adding the optics.

But to my question.

What steps should I take to zero in the new sights.

Should I put the new rear flip up rear on and then zero with the original front sight or put both new ones on and go from there.

What sight should adjust first or does it matter.

LOL...Hopefully my initial shots will hit paper.

Never replaced non-optic sights before.

Thanks in advance.

10-96 · September 12, 2010, 09:09 AM

What I've done, is to mark (index) the barrel in relation to the gas hole, then find center on the new gas block and mark it. It's much easier to align the holes when you have marks to go by. Then with the sights in place, center them up (square on the rear, and flush-base on the front), then you can "eyeball" it to get it close. Take a piece of paper, make a 2" black dot and 2" below that, make a 4" black dot (2" apart from edge to edge). Place the upper on a solid rest and hang the paper approx 20 feet away. Center the 4" dot in the bore and walk your sights to the 2" dot. When done real careful like, this will get you on paper at 25yds. You can buy a laser chamber insert for $20 to $25 and do the same thing. Just remember, these will get you close, but not dead-on.

Also, when putting on the gas block, if you're not sure about your indexing marks or hole alignment, try this... Take a fired case and make two or three wraps around it with electrical tape and 'lightly' insert it into the chamber. With the BCG removed, blow into the muzzle end. When blowing, place a finger over the receiver end of the gas tube. If you have bad hole alignment- you wont feel/hear any air. Also, if you don't have that metal cap that holds the muzzle end of removable handguards, you'll have to keep the new gas block 7/32" away from the barrel shoulder for proper hole alignment. If you have that metal part and removable handguards then don't worry- just butt the gas block up tight against the cap.

**Unclenick** · September 12, 2010, 09:31 AM

The law of independence of variables means changing either sight is the same as any other sight change. So I would put both sights on at once. Otherwise you're zeroing twice.

After the gas block alignment (above suggestions are all good), I can tell you what I do for the sighting itself: I put a big target, like a pistol target, at 25 yards and put a laser bore sighter in the barrel and adjust the sights until they are on the laser. I then remove the laser and shoot a few rounds at that same range to get the windage correct (the lasers are never exact). If you hit exactly to point of aim at 25, you won't be off more than a few inches at 100 yards. I then go to 100 yards with the same target and fine tune the settings.

If you don't have the laser bore sighter, you can still pull the bolt and carrier and set the rifle on bags and position it so you see the bullseye centered in bore. This is called bore sighting. You then alternately look through the bore and the sights, adjusting the sights until they seem to be looking where the bore is looking. It won't be exact, but it will get you on the paper close enough at 25 yards to adjust the windage and initial elevation same as with the laser, then go to 100 yards to correct the last few inches.

Even if bore sighting proves awkward for you or you don't have a bench, you can always start with the big paper very close, like 25 feet, and set the sights until the windage is right and you hit an inch or two low, then go to 25 to tune it a little tighter, then go to 100 yards. If you set it to hit two inches high at 100 yards, you will about be on at 200 and 300 will require maybe 8" of holdover or so.

TXGunNut · September 12, 2010, 09:45 AM

Don't forget-I generally do

-move the rear sight the direction you want the bullet to go. Move the front sight in the opposite direction.

dontcatchmany · September 12, 2010, 12:00 PM

Thanks folks.

Never having done this I was not able to get my brain to "walk" through the steps...I can see clearly now....almost.

Thanks again.

All my stuff should be in tomorrow and I can start to work. Heck even got a couple thousand rounds of ammo that should be here Tuesday.

TXGunNut · September 12, 2010, 08:08 PM

Sounds like a party to me.

Lots of little boxes full of high-tech goodies and big heavy boxes with hundreds and hundreds of shiny bits. Have fun!

September 12, 2010, 08:50 AM	#1
dontcatchmany Senior Member Join Date: July 19, 2010 Posts: 460	Zeroing in new front and rear sights I am getting a new M&P 15R which has no rear iron sight. I am intending to put on the Magpul rear flip up sights and replacing the M&Ps original front sight with a Magpul front flip up....as well as a different gas block. I will eventually put on optics that have a true cowitness(gosh I do not like that term) with the flip ups when needed. My initial goal is to thoroughly familiarize my self with and become competent in using the "iron" (actualy polymer) sights prior to adding the optics. But to my question. What steps should I take to zero in the new sights. Should I put the new rear flip up rear on and then zero with the original front sight or put both new ones on and go from there. What sight should adjust first or does it matter. LOL...Hopefully my initial shots will hit paper. Never replaced non-optic sights before. Thanks in advance.

September 12, 2010, 09:09 AM	#2
10-96 Senior Member Join Date: October 19, 2005 Location: Tx Panhandle Territory Posts: 4,160	What I've done, is to mark (index) the barrel in relation to the gas hole, then find center on the new gas block and mark it. It's much easier to align the holes when you have marks to go by. Then with the sights in place, center them up (square on the rear, and flush-base on the front), then you can "eyeball" it to get it close. Take a piece of paper, make a 2" black dot and 2" below that, make a 4" black dot (2" apart from edge to edge). Place the upper on a solid rest and hang the paper approx 20 feet away. Center the 4" dot in the bore and walk your sights to the 2" dot. When done real careful like, this will get you on paper at 25yds. You can buy a laser chamber insert for $20 to $25 and do the same thing. Just remember, these will get you close, but not dead-on. Also, when putting on the gas block, if you're not sure about your indexing marks or hole alignment, try this... Take a fired case and make two or three wraps around it with electrical tape and 'lightly' insert it into the chamber. With the BCG removed, blow into the muzzle end. When blowing, place a finger over the receiver end of the gas tube. If you have bad hole alignment- you wont feel/hear any air. Also, if you don't have that metal cap that holds the muzzle end of removable handguards, you'll have to keep the new gas block 7/32" away from the barrel shoulder for proper hole alignment. If you have that metal part and removable handguards then don't worry- just butt the gas block up tight against the cap. __________________ Rednecks... Keeping the woods critter-free since March 2, 1836. (TX Independence Day) I suspect a thing or two... because I've seen a thing or two.

September 12, 2010, 09:31 AM	#3
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	The law of independence of variables means changing either sight is the same as any other sight change. So I would put both sights on at once. Otherwise you're zeroing twice. After the gas block alignment (above suggestions are all good), I can tell you what I do for the sighting itself: I put a big target, like a pistol target, at 25 yards and put a laser bore sighter in the barrel and adjust the sights until they are on the laser. I then remove the laser and shoot a few rounds at that same range to get the windage correct (the lasers are never exact). If you hit exactly to point of aim at 25, you won't be off more than a few inches at 100 yards. I then go to 100 yards with the same target and fine tune the settings. If you don't have the laser bore sighter, you can still pull the bolt and carrier and set the rifle on bags and position it so you see the bullseye centered in bore. This is called bore sighting. You then alternately look through the bore and the sights, adjusting the sights until they seem to be looking where the bore is looking. It won't be exact, but it will get you on the paper close enough at 25 yards to adjust the windage and initial elevation same as with the laser, then go to 100 yards to correct the last few inches. Even if bore sighting proves awkward for you or you don't have a bench, you can always start with the big paper very close, like 25 feet, and set the sights until the windage is right and you hit an inch or two low, then go to 25 to tune it a little tighter, then go to 100 yards. If you set it to hit two inches high at 100 yards, you will about be on at 200 and 300 will require maybe 8" of holdover or so. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; September 12, 2010 at 09:36 AM. Reason: typo fixes

September 12, 2010, 09:45 AM	#4
TXGunNut Senior Member Join Date: January 16, 2010 Location: If you have to ask... Posts: 2,860	Don't forget-I generally do -move the rear sight the direction you want the bullet to go. Move the front sight in the opposite direction. __________________ Life Member NRA, TSRA Smokeless powder is a passing fad! -Steve Garbe I hate rude behavior in a man. I won't tolerate it. -Woodrow F. Call Lonesome Dove My favorite recipes start out with a handful of used wheelweights.

September 12, 2010, 08:08 PM	#6
TXGunNut Senior Member Join Date: January 16, 2010 Location: If you have to ask... Posts: 2,860	Sounds like a party to me. Lots of little boxes full of high-tech goodies and big heavy boxes with hundreds and hundreds of shiny bits. Have fun! __________________ Life Member NRA, TSRA Smokeless powder is a passing fad! -Steve Garbe I hate rude behavior in a man. I won't tolerate it. -Woodrow F. Call Lonesome Dove My favorite recipes start out with a handful of used wheelweights.

September 12, 2010, 12:00 PM	#5
dontcatchmany Senior Member Join Date: July 19, 2010 Posts: 460	Thanks folks. Never having done this I was not able to get my brain to "walk" through the steps...I can see clearly now....almost. Thanks again. All my stuff should be in tomorrow and I can start to work. Heck even got a couple thousand rounds of ammo that should be here Tuesday.