.223 vs 5.56x45 accuracy
Well two questions actually.
1. Is 5.56x45 more accurate than .223 from a 5.56 chambered AR, or should accuracy be the same?
2. Anyone notice or have this issue, or can explain it: With .223 (Remington 55gr fmj) say you get your sights/scope set at 50 feet (just to get on paper) then move target out to about 80 yards and you have to bring the sights "down" 6 inches or more. (80 yards was all I had to work with). Should have to go "up" not down.
Accuracy should be about the same. It will depend more on the actual round (including bullet weight and shape, and powder type and rifling twist) than anything.
One issue with the AR style rifle is the height of the sights above the bore axis. You can zero the sights in at 25 yards, and the round will cross the plane of the sights again at 200 200 yards.
50 feet sounds awfully close for the sights to be zero'd at. With how most AR's are sighted, the round still hasn't crossed the plane of the sights at that distance.
I zero my AR at 36 yards/300 yards - at 7 yards, I have to put the sights 2.5 inches higher than where I want the bullet to hit.
As for accuracy - you won't be able to notice a difference unless you're shooting groups from the prone and are a very good shot.
From view the below YouTube it appears that zeroing at 50 yards seems to be the most applicable... you decide...
AR15 Zero: Introduction - YouTube
The same thing happened when zeroing the scope on my 10/22. I started at 15 yards to get it on paper, then moved out to 30 where I wanted to dial it in. I had to move the POI down several inches to hit on center at 30 yards. This is due to physics and the arc shaped trajectory of the bullet. At 15 yards, the bullet had not yet reached the apex of the trajectory. The 30 yard shot allowed the bullet to climb a little bit higher on the trajectory arc. The same general idea would apply with the .223.
Originally Posted by tkruf
tkruf; what you are experiencing is the trajectory of a .223/5.56 round. Please refer to the link below which explains very well how the trajectory of standard 556 and 223 rounds relate to line of sight. For this reason many have adopted the 50yard/200meter zero, also known as the Santose Improved Battle Zero as it offers a very good trajectory to line of sight aiming scheme.
AR-15 Zeros and Trajectories - AR15.COM
Edit: I think that's what your talking about anyways, because if you zero your AR at roughly 15 yards you will be shooting about 4-6 inches high at 80 yards. Requiring you to aim low.
If it's 5.56 ammo, accuracy should be about the same.
The difference in accuracy between 5.56 and .223 is more about how the chamber is cut. A true .223 chamber has a shorter distance from the case neck to where the rifling starts. A 5.56 chamber has a longer distance between the two areas. This distance is called the leade or throat.
A shorter throat can improve accuracy because that is less space for the bullet to 'bounce' around between the case neck and the rifling when fired.
A chamber with a shorter throat (.223) also will usually have higher chamber pressures than a chamber with a longer throat (5.56).
This is also why you shouldn't fire 5.56 (normally higher pressures) in a .223 chamber. It's the lengthened leade/throat in the 5.56 chamber that helps sedate the spike in pressure when the bullet contacts rifling. A .223 chamber does not have this.
I zero at 25 yards with an MA tech BUIS. Then I can adjust it from 200 yards out to point of aim point of impact.
Here we go again. If your going to zero an AR at 25 meters you use a 25 meter zero target or draw the box in your self . Zero it then aim as normal your on.
If you shoot .223 zero for it if you shoot 5.56 zero for it either one you will hit the target it is not a sniper rifle it was never meant to be one no madder what round you fire.
FM 3-22.9 Rifle Marksmanship M16A1, M16A2/3, M16A4, M4 CARBINE
I was thinking the same thing. Seems to be the most useful at 50yd zero. Great video BTW, thanks!
Originally Posted by Crowman
There is no "arc" to the trajectory of the bullet. It goes straight for a while, and then starts to fall down. Based on how your sights are adjusted (the range you choose to zero your sights) your rifle will have the sights parallel to the ground in line with the target - your barrel will be angled upwards slightly. This creates the illusion of an "arc" path for the bullet. In reality, you are angling the barrel up. So as the bullet leaves going straight, it goes above the parallel line of your sights with the target and the ground. Later in the bullets flight path, as it starts to lose velocity and gravity is pulling it downward, it will cross the parallel line of your sights and the target again.
You can choose the ranges the bullet will cross the parallel line of your sights. If you zero your rifle at 50 feet - you will be hitting "high" all the way until you get to 500 yards. This is a "bad" zero - because although you will be able to hit accurately at 50 feet (and 500 yards), your barrel will be angled upward at such an extreme angle, that at 300 yards your impacts will be 20 inches high. At 80 yards you'll be 8 inches high. This is why it's a "bad" zero.
If you zero at 25 yards - you'll be "on" at 25 yards, and at about 350 yards. In between these ranges, you'll be "high" - with the worst being about 10 inches high at 200 yards.
36 yds/300 yds, you'll be high 4 inches at 150 yards.
50/200, high 1.7 inches at 165 yards.
100/110 - that's it. you're low between point blank and 100, and you're low everywhere else too.
When I was in the Marines and issued an M16 - it has a rear sight that is designed to be zero'd at 36/300. This means your rifle is sighted in to shoot "point blank" out to 300 yards - sure you'll be 4 inches high at 150 yards - but 4 inches high is still a hit on a man sized target. Also - I have the LMT rear sights on most of my ARs - which uses the same elevation adjustments and design as the service rifles.
There are pros and cons to each zero. Also - the numbers I just quoted you are based on a 62 grain bullet with a BC of .304 going 3000 fps - everything changes when you change ammo.
Next time you go out and want to get your sights "on paper" at 50 feet - try using 1.5 inches below your point of aim as a desired point of impact. This will make your zero adjustments easier. The best thing to do is to choose which zero you want to use, set your sights for that, and then understand that you're going to be +/- a few inches pretty much everywhere.
If you want to calculate the ballistics of your own ammo, you'll need to know the muzzle velocity (actual from your rifle/barrel length, not what's written on the box), the ballistic coefficient of the bullet itself, and the exact height of your sights above the centerline of the bore (front sight).
Most people don't go through all the trouble of doing this, and just choose if they want a 25/350 zero, with 10 inches of "play", 36/300 w/ 4", or 50/200 w/ 1.7".
The 50 yard zero makes a lot of sense, as long as you practice holdover at longer ranges and know the drop of your round. I choose the 36 because it's what I'm used to, and my sights are designed for it.
Good luck with whatever you end up choosing. And if you want to calculate your ballistics, here's a tool for you: Handloads.Com Ballistic Calculator
What you described here is indeed an arc in the bullet path, and it is no illusion. With the barrel angled upward, the bullet leaves the barrel at that same upward angle and travels along that path, losing velocity, until the downward force of gravity neutralizes the slightly upward force of the bullet at the apex of the arc. After reaching the apex of the arc, the downward force of gravity and loss of velocity continue to cause the bullet to drop. It's not a huge sweeping arc, but it's not linear.
Originally Posted by aus71383
Now if the barrel was held perfectly parallel to the ground, the bullet path would still be somewhat arc shaped, only with no initial upward angle. The bullet would leave the barrel along that same parallel line before gravity almost immediately started forcing it downward. The bullet drop would not be perceptible at point blank range, but outside of point blank range for a given firearm/cartridge combo the constant drop in velocity coupled with the force of gravity would make bullet drop more pronounced at increasing ranges. Therefore, in the vast majority of instances (outside of point blank range), a change in barrel elevation/angle is necessary for precision shooting even if it is only a very minute adjustment, and an arc shaped bullet path with intial upward movement is produced.
Thanks for the explanations and great links. Now it all makes sense. :) The area where I do most of my shooting, I do not have 200 yards. I barely have 100 yards in the best direction. I like both the 36/300 and the 50/200 zero but am leaning toward the 36/300. I will have to go measure out 36 yards and re-zero it when I get a chance.
A bullet dropped from your hand will hit the ground at the same time as a bullet fired from a muzzle parallel to level ground. Science is amazing. This is why we "throw" them "up" with the barrel. How high you throw it is up to you. RT is right - for precision shooting, you will need to know the bullet path.
For combat or "point blank" shooting, a good zero is "good enough" - especially with the relatively flat trajectory of the .223/5.56x45
Aus you are correct about the bullet itself not 'creating' an arc, we do that with our barrel, but nonetheless most people just accept the fact whatever the reason, the bullet has an arc to it.