M4 Sight-in Distance?

[iratollah]

At what distance do you sight in your M4? A LEO pal says they use 25 yds for their holo sights because most of their work is CQB. He also says .223 ballistics do odd things at 50 and 100 when you're sighted in for 25.

Are most of you, especially those using reflexive sights using longer distances for TEOTWAWKI or zombie scenarios?

Just curious.

[The Annoyed Man]

With the 55 grain M193 bullet, zeroing at 25 yards will also give you a 250 yard zero. The bullet is ascending through the point of aim at 25 yards, and descending through the point of aim at 250 yards. So at 100 yards, the bullet is somewhere near the top of its arc, about 3 or 4 inches high of the point of aim. Figured into these calculations is the fact that the line of sight is approximately 2.25" or so above the bore axis. That means that, at very close ranges, such as CQB ranges, bullet impact is going to be 2.25" lower than point of aim - critical in hostage scenarios - because the distance to the muzzle is so close that the bullet has barely begun its climb to the line of sight on its way to apogee.

I zero my carbine at 25 yards using an EOTech sight.

Does that answer your question?

[MoJo]

Traditional military and LE doctrine is to zero at 25 METERS not yards. Recently this doctrine is changing to zero at the actual range you want your primary zero for. So, if you want point of aim/point of impact to be at 100 yards, zero at 100 yards. Back when I was a ground pounder in the 1960s we zeroed 2" high at 25 meters with the short aperture and we were good to go out to about 250 flip up the tall aperture and GTG out to 350-400.

All this is contingent on actually shooting at various ranges to verify your rifle/sight/ammo combination will perform like you want it to.

[OldCannon]

Um, TAM, do you reverify zero at 250yds? I've always found that difficult with my EOTech

[Medic218]

Um, TAM, do you reverify zero at 250yds? I've always found that difficult with my EOTech

not with a 100x magnifier and bi-focals!

[The Annoyed Man]

Um, TAM, do you reverify zero at 250yds? I've always found that difficult with my EOTech

Unfortunately, I haven't been able to reverify for lack of a range nearby with that kind of distance. As far as the EOTech, I do have a 3X magnifier, but I don't expect that I would be much use with it at 250 yards - particularly with my eyes. But that said, I would like to see if I can get a good 100 yard zero with that setup. I just hadn't done so yet because my first trips to the range were with FMJ ammo, and that restricted me to the 25 yard tactical bay.

[gigag04]

I go to a carbine school tue-wed. I'll let you guys know what the consensus is at an LEO only training environment. There are some shooters teaching so it should be a good time.

[aaronspuler]

This 25m zeroing target might be of some assistance.

http://www.spuler.us/gunsandammo/?p=253" onclick="window.open(this.href);return false;

[Mando'a]

I used this resource, when I zeroed my M4 at 25m.

http://sites.google.com/site/jimmyhots/usmc25mar-15zero" onclick="window.open(this.href);return false;

It has pictures, and goes step-by-step. Which is great for a chowder-head like me.

Also, I don't remember where I found it, but google "25 meter zeroing target M4 carbine"
(I'm assuming you have a carbine)

[Chuck TX]

I prefer a 50/200 zero for its flatter trajectory. That's is, zeroed at 50 yards which depending on the particular loading will fall around zero at 200 yards give or take. It's the flattest trajectory you'll get between 0-200 yards with the greatest deviation being ~2.25"+/-. It's about 1.2" low at 25 yards.

A 25yard zero will be near zero at 300 yards with M855 (62gr) and a little further with M193 (55gr). It'll be about 5" high around 100 yards and be 7-9" high during the arc at about 175-200 yards depending on the load. It's great for shooting at 25 yards and under, but the trajectory starts climbing fast.

Of course, it will vary a little depending on barrel length and twist rate.

[gigag04]

Our dept is at 25 yds using the circle with a black rectangle in the top of it target (someone will know what I'm talking about).

We follow pretty much what TAM said. 2" high at 25yds.

[jimlongley]

Back in my day, also in the 60s, we called a 25 meter zero "1000 inch range" and it's nice to see it hasn't changed much. I still use it on my long guns when I don't have room enough to get a battle zero.

I would dearly love to know what "odd things" your LEO friend thinks happen at 50 and 100 yards.

[Chuck TX]

By "odd things" I'd wager they mean the bullets trajectory.

This is with a 1/7 twist 14.5" barrel shooting M193, but you get the idea.

[jimlongley]

By "odd things" I'd wager they mean the bullets trajectory.

This is with a 1/7 twist 14.5" barrel shooting M193, but you get the idea.

Thus, if I am aiming COM with my 25 yard zeroed rifle, I can pretty much assure a hit at any range between 0 and 400. If you run the chart out to 200 and beyond, the graph starts to go back up again.

The "odd things" comment was a wonderment based on converstaions with people who do not understand the first thing about external ballistics, such as those who have absolutely no clue that the bullet's path leaves the sight line much less rises above it. I was having a conversation, recently, with a co-worker who informed me that the .338 Lapua shot "so fast" (?) that the bullet didn't actually start to drop until it was 1000 yards from the muzzle. I tried to explain the difference between "flat shooting" and his concept, but he refused to even consider that a bullet starts to drop, due to the effects of gravity, the instant it leaves the muzzle. This same worthy later ascribed the same ballistic characteristic to a "new" .50 caliber rifle invented by some guy named Barrett.

The "idea" is absolutely clear to me, and has been for more thann 50 years, it's propogating it to others that is important.