How to adjust/use elevation on M4A2 rifle?

Full Metal Jacket · October 3, 2008, 06:12 PM

So say I have an M4A2 zeroed at 50 yards, with the rotating elevation cylinder's line matching up with the "z" on the cylinder (thats what you do, right?), what purpose does the "8/3" mark serve?

So say I hit the bullseye at 50 yards with the "Z" elevation setting, and I want to shoot at 150, 200, 250, 300, or 350 yards? If I can calculate the MOA bullet drop with a ballistics calculator, how do I apply this to the elevation cylinder?

BTW, on a side note, the gun should be zeroed using the small aperature, and then after that I can use either, right?

TheManHimself · October 3, 2008, 06:52 PM

Essentially, you want the small aperture zeroed for 300m with the drum on 8/3. As you rotate the drum you'll see numbers, 4, 5, 6, 7, until you get back round to 8/3. That's your rough elevation adjustment in hundreds of meters. It's not going to be target-accurate, just an estimation that's close enough for combat usage, and you have to be using the standard-issue military round (62gr projo, ballistic coefficient .304, running around 3100fps from a 20" barrel) for the trajectory to line up right.

Oh, and this assumes your sight is actually made to the correct specs. There are A2 uppers and A4 carry handles out there using the wrong thread pitch in the elevation screw (because apparently some bargain-basement manufacturers can't even follow the most basic design specs), the end result being that the clicks on the wheel don't correspond to anything.

Full Metal Jacket · October 3, 2008, 07:58 PM

Ok, thanks.

So say with a 50 yard zero firing M193, the elevation numbers basically mean crap, and I cant adjust for elevation any other way?

Not that I care, since with a 50/200 zero, i can hit out to 250 yards with no holdover.

TheManHimself · October 4, 2008, 11:50 AM

The large aperture is meant for 0-200m when the elevation wheel is on the 8/3 setting. If you do the 50yd/200m IBZ with the large aperture, your elevation wheel settings should be close to correct for the small aperture.

Edit: and as far as using M193 as opposed to the current military M855 round, since the elevation wheel on an A2 upper is intended for a 20" barreled M16A2, the reduced velocity of firing M193 from an M4-length barrel should even out the differences in trajectory.

Edit #2: After playing with some ballistics software and counting the clicks on an A2 upper, it looks like the elevation clicks on a mil-spec A2 upper are approximately 1MOA

Full Metal Jacket · October 4, 2008, 01:01 PM

Cool. So when im shooting 0-250 I just leave the elevation wheel on "8/3" and when shooting farther, each number click (1,2,3,4 etc) moves the point of impact 1 MOA higher in order to compensate for drop?

And should I zero the gun at 50 yards with the 8/3 setting or the "z"?

TheManHimself · October 15, 2008, 05:57 PM

Sorry to be so late in replying, but...

It's each individual "click" that's around 1MOA of adjustment. The numbers themselves are several clicks apart - so that going from the 500m to the 600m setting, for example, moves the rear sight up the proper number of ~1MOA clicks.

And that's not a "z" (Or shouldn't be, unless something is really funky with your upper), it's a 5. Or maybe a 7. None of the markings on the Colt A2 upper I'm playing with right now look much like a "z".

But back to the point, if you want to use the 50y/200m zero, and keep the elevation adjustments correct, you'll want to use the large hole aperture for that zero. When zeroed that way, flipping over to the small aperture without touching the elevation wheel will be a roughly 300m zero; from there turning the wheel up the the "4" will be your 400m zero, the "5" 500m, and so on.

If yours doesn't work the way I describe, then it's one of the "incorrect thread pitch" A2 sights like I mentioned earlier; in which case zero on whatever setting you want because the numbers and clicks are meaningless.

ISC · October 15, 2008, 06:13 PM

this should help

IIRC The M4 should have a 6/3 setting instead of 8/3 (like a A2 with a 20" barrel) due to the difference in ballistics. Of course a M4 has a 14.5" barrel and I assume your rifle has a 16" barrel.

Bartholomew Roberts · October 16, 2008, 10:25 AM

The M4 uses a 6/3 instead of 8/3 because the space for the detachable carry handle means it can't take a long enough screw to adjust to 8/3.

You mentioned you have an A2 upper (fixed carry handle) so yours should say 8/3.

If you visit the Maryland AR15 Shooters Site and check out the 'Improved Battle Zero' - they show you how to use a 50m zero with the small aperture and large aperture and still have use of the elevation wheel to 550m. You will need a small allen wrench to tweak the elevation drum though.

Alternatively you can sight in at 25m using the military method of zeroing. This will give you a 200m zero on the large aperture (very close to a 50m zero) and a 300m zero (or whatever the wheel is dialed to) for the small aperture.

I am not a big fan of the military zero because it is sometimes nice to be able to use the smaller aperture at closer distances and you can hit as much as 5-6 inches high at 100 with a 300m zero. If you know you won't be shooting at anything shorter than 40 inches tall though (silhouettes) then the military zero works fine.

maestro pistolero · October 16, 2008, 12:39 PM

These are the best and most complete instructions for setting up an AR with an Improved Battlesight Zero. I have set up two rifles this way (1 M4 and 1 M16A2):

http://groups.msn.com/TheMarylandAR1...sightzero.msnw

There's one more twist to this if you want to shoot at POA at 100 yards.

http://www.ar15.com/forums/topic.html?b=3&f=18&t=328143

Good Luck!

October 3, 2008, 06:12 PM	#1
Full Metal Jacket Senior Member Join Date: December 8, 2004 Posts: 260	How to adjust/use elevation on M4A2 rifle? So say I have an M4A2 zeroed at 50 yards, with the rotating elevation cylinder's line matching up with the "z" on the cylinder (thats what you do, right?), what purpose does the "8/3" mark serve? So say I hit the bullseye at 50 yards with the "Z" elevation setting, and I want to shoot at 150, 200, 250, 300, or 350 yards? If I can calculate the MOA bullet drop with a ballistics calculator, how do I apply this to the elevation cylinder? BTW, on a side note, the gun should be zeroed using the small aperature, and then after that I can use either, right?

October 16, 2008, 12:39 PM	#9
maestro pistolero Senior Member Join Date: August 16, 2007 Posts: 2,153	Here's how These are the best and most complete instructions for setting up an AR with an Improved Battlesight Zero. I have set up two rifles this way (1 M4 and 1 M16A2): http://groups.msn.com/TheMarylandAR1...sightzero.msnw There's one more twist to this if you want to shoot at POA at 100 yards. http://www.ar15.com/forums/topic.html?b=3&f=18&t=328143 Good Luck!

October 3, 2008, 06:52 PM	#2
TheManHimself Senior Member Join Date: March 25, 2008 Posts: 730	Essentially, you want the small aperture zeroed for 300m with the drum on 8/3. As you rotate the drum you'll see numbers, 4, 5, 6, 7, until you get back round to 8/3. That's your rough elevation adjustment in hundreds of meters. It's not going to be target-accurate, just an estimation that's close enough for combat usage, and you have to be using the standard-issue military round (62gr projo, ballistic coefficient .304, running around 3100fps from a 20" barrel) for the trajectory to line up right. Oh, and this assumes your sight is actually made to the correct specs. There are A2 uppers and A4 carry handles out there using the wrong thread pitch in the elevation screw (because apparently some bargain-basement manufacturers can't even follow the most basic design specs), the end result being that the clicks on the wheel don't correspond to anything.

October 3, 2008, 07:58 PM	#3
Full Metal Jacket Senior Member Join Date: December 8, 2004 Posts: 260	Ok, thanks. So say with a 50 yard zero firing M193, the elevation numbers basically mean crap, and I cant adjust for elevation any other way? Not that I care, since with a 50/200 zero, i can hit out to 250 yards with no holdover.

October 4, 2008, 11:50 AM	#4
TheManHimself Senior Member Join Date: March 25, 2008 Posts: 730	The large aperture is meant for 0-200m when the elevation wheel is on the 8/3 setting. If you do the 50yd/200m IBZ with the large aperture, your elevation wheel settings should be close to correct for the small aperture. Edit: and as far as using M193 as opposed to the current military M855 round, since the elevation wheel on an A2 upper is intended for a 20" barreled M16A2, the reduced velocity of firing M193 from an M4-length barrel should even out the differences in trajectory. Edit #2: After playing with some ballistics software and counting the clicks on an A2 upper, it looks like the elevation clicks on a mil-spec A2 upper are approximately 1MOA

October 4, 2008, 01:01 PM	#5
Full Metal Jacket Senior Member Join Date: December 8, 2004 Posts: 260	Cool. So when im shooting 0-250 I just leave the elevation wheel on "8/3" and when shooting farther, each number click (1,2,3,4 etc) moves the point of impact 1 MOA higher in order to compensate for drop? And should I zero the gun at 50 yards with the 8/3 setting or the "z"?

October 15, 2008, 05:57 PM	#6
TheManHimself Senior Member Join Date: March 25, 2008 Posts: 730	Sorry to be so late in replying, but... It's each individual "click" that's around 1MOA of adjustment. The numbers themselves are several clicks apart - so that going from the 500m to the 600m setting, for example, moves the rear sight up the proper number of ~1MOA clicks. And that's not a "z" (Or shouldn't be, unless something is really funky with your upper), it's a 5. Or maybe a 7. None of the markings on the Colt A2 upper I'm playing with right now look much like a "z". But back to the point, if you want to use the 50y/200m zero, and keep the elevation adjustments correct, you'll want to use the large hole aperture for that zero. When zeroed that way, flipping over to the small aperture without touching the elevation wheel will be a roughly 300m zero; from there turning the wheel up the the "4" will be your 400m zero, the "5" 500m, and so on. If yours doesn't work the way I describe, then it's one of the "incorrect thread pitch" A2 sights like I mentioned earlier; in which case zero on whatever setting you want because the numbers and clicks are meaningless.

October 15, 2008, 06:13 PM	#7
ISC Junior member Join Date: August 5, 2007 Location: Florida Posts: 1,982	this should help IIRC The M4 should have a 6/3 setting instead of 8/3 (like a A2 with a 20" barrel) due to the difference in ballistics. Of course a M4 has a 14.5" barrel and I assume your rifle has a 16" barrel.

October 16, 2008, 10:25 AM	#8
Bartholomew Roberts member Join Date: June 12, 2000 Location: Texas and Oklahoma area Posts: 8,462	The M4 uses a 6/3 instead of 8/3 because the space for the detachable carry handle means it can't take a long enough screw to adjust to 8/3. You mentioned you have an A2 upper (fixed carry handle) so yours should say 8/3. If you visit the Maryland AR15 Shooters Site and check out the 'Improved Battle Zero' - they show you how to use a 50m zero with the small aperture and large aperture and still have use of the elevation wheel to 550m. You will need a small allen wrench to tweak the elevation drum though. Alternatively you can sight in at 25m using the military method of zeroing. This will give you a 200m zero on the large aperture (very close to a 50m zero) and a 300m zero (or whatever the wheel is dialed to) for the small aperture. I am not a big fan of the military zero because it is sometimes nice to be able to use the smaller aperture at closer distances and you can hit as much as 5-6 inches high at 100 with a 300m zero. If you know you won't be shooting at anything shorter than 40 inches tall though (silhouettes) then the military zero works fine.