On the M16 rifle (or perhaps any other rifle) the aperture and sight tip (used to aim at the target) are positioned above the muzzle of the rifle. Why is this so? If one were pointing the muzzle at an object, the aperture and sight tip would then be aligned above the object.
Yes, if the bullet behaved like a beam of light. Which it doesn’t. The sights are aligned to show where a bullet will hit, given a known muzzle velocity. Thus the sights are actually aimed at a point below the muzzle, to allow for droop due to gravity.
If the peep sight and front sight post were pointed straight at the bullseye, the axis of the barrel points above the bullseye, or is oriented upwards. The bullet will cross the “line of sight” twice, once going up, and once coming down. An accurate zeroing at 25 yards, for instance, is also accurate at 200 yards.
If I remember my army basic training right, the sights are supposed to be aligned to hit at 25 yards (as the bullet is rising to meet the sight picture) and 250 yards (as it is descending), having reached a sort of apex at 150 yards. So for a target at 300 yards, aim a little high, and for a target at 150 yards, aim a little low. This is kind of hard to explain with words, I wish I could draw a diagram on a cocktail napkin.
We zeroed our sights in at 25 yards.
My recollection of these facts and figures are colored by 16 years of disuse.
I see on preview that UncleBill has registered much the same thing I have. His 200-yard figure is probably correct.
Droop, eh? Sorry, I couldn’t resist. If you think about it, optimystique, all sights are above the centerline axis of the bore of a handheld firearm. Until some innovative person comes up with a way to sight through the bore (sorta like a SLR camera, perhaps), we are stuck with the physics of having to use some exterior aiming device.
I think Q.E.D. and UncleBill both understand the way rifle sights work, but it is sometimes difficult to explain. Suffice it to say that one must adjust the sights so that they are aligned to the spot that the bullet strikes at a given distance. The rifleman must then calculate where to aim the sights at distances greater than or less than this “zero” range. For example, it is usually appropriate to “sight in” rifles with a telescopic sight for a “zero range” of 200 yards. This means that the bullet will strike the target at exactly the point that is aimed at for a distance of 200 yards. For shorter distances - 100 yards, for instance - you will actually have to aim at a point lower than where you want the bullet to strike. And, of course, you would have to aim at a point higher than your intended strike point if the range is greater than 200 yards.
Many riflemen will create a “range card” that they tape to the rifle stock which gives the bullet drop for ranges from 100 to 500 yards. The real trick to accurate shooting is to correctly estimate the range to target. How many times have you heard something similar to this: “Yeah, I made one helluva shot on that whitetail. He was out there at 600 yards when I dropped him right where he stood.” A shot at a whitetail deer at 600 feet is a pretty decent shot! I shoot a .308 Winchester a lot. With the very best ammo I can manufacture, I have to “hold over” 54 inches when shooting at targets at 500 yards. I would estimate that a shot at 600 yards would require me to “hold over” about 100 inches. Possible, I reckon, but I’m not going to take a shot at game at that distance. Did I mention that I shoot .308 Winchester a lot? And the best bullet that I load in that caliber probably isn’t real good for hunting, anyway - it’s the Sierra 168 grain HPBT.
Sorry if I rambled on about this - it’s one of my favorite subjects. There’s lots of technical stuff about this that probably isn’t interesting to most of the folks here.
A sight through the bore would never work, as the POI would always be lower than what the sight is aimed at.
Unclebill is correct. Stated another way:
A lot of people (including a lot of shooters) believe that the barrel is pointed at the target and the sights are adjusted above or below (or side to side of) the target.
But the opposite is true. When you “adjust the sights” for a fixed target distance, you are not adjusting the sights. The sights are always on-target, so there’s no reason to adjust the sights. When you “adjusting the sights” you are really adjusting the angle of the barrel.
In the case of an elevation adjustment, the sights are on target and the angle of the barrel is adjusted so it points up. When the bullet leaves the barrel, it intersects the line of sight a few feet in front of the barrel. Immediately after this happens the bullet is traveling above the line of sight. After a while, the bullet reaches the apex and starts to fall. Sooner or later it will fall to the point where it (again) intersects the line of sight. If the angle of the barrel is adjusted correctly, the bullet will intersect the line of sight precisely at the target location.
Huh?
I guess I explained that poorly. You know, of course, that the bullet falls as it flies forward, so in order to hit a given point, you need to aim higher than it. Thus the sights are adjusted so that when you’re looking through them, you’re looking at a point slightly below where the gun barrel is actually pointing at. Is that a bit clearer?
Perhaps this illustration of a bullet path will help.
Note that angles and dimensions are grossly exaggerated for clarity. The sights, be they aperture and post or notch and post or a telescope are aligned to the target at an angle to the center line of the barrel. The bullet path crosses once near the rifle and once at the target.
The M-16 has a line of sight unusually high above the barrel due to its design. There is a spring loaded buffer in the buttstock directly in line with the barrel. Because of this the comb of the stsock, where the shooter’s cheek rests, cannot be dropped in relation to the barrel centerline. Since the shooter’s eye is a couple of inches above the cheekbone that’s where the sights have to be placed.
Yes. But I’d like to add that you are always aimed directly on the target. The barrel on the otherhand is pointing above the target…
The reason the sights are so high is because Eugene Stoner (the designer, not the former Doper) wanted to put the barrel in line with the stock so that there would be less muzzle rise on recoil which would result in a quicker re-aquisition of the target.
While you are correct for the part of the flight when the round is falling, if you are zeroed at 200yds/25yds (I am also going from very foggy memory, so don’t quote me on these ranges) and you fire at a target 15 yards away (before the first intersection), you are aiming at a point above the axis of the barrel.
Crafter_Man, you are always aiming sights at the target if they are adjusted properly for the given range, but if you are adjusted for 200 yds, and a target pops up at 300 yds, you don’t adjust the front sight post, you aim high. The beauty of adjustable sights is dialing in the perfect angles of the weapon for point of impact at a given range (actually almost always two ranges), but at a different range, say 100yds further, Kentucky Windage comes into play unless you adjust sights. Padeye’s link shows this well.
Very good point, which I failed to mention. Padeye’s diagram shows this quite well.
That was poorly edited. Please diregrard the first paragraph and replace it with:
“While you are correct for the majority of the path of the round, if you are zeroed at 200yds/25yds (I am also going from very foggy memory, so don’t quote me on these ranges) and you fire at a target 15 yards away (before the first intersection), you are aiming at a point above the intersection of the axis the barrel and the target.”
Back to the OP: Yes, optimystique, you are right. If the rifle is held parallel to the ground and the sights are set at zero elevation and zero windage (assuming the sights are mounted parallel to the ground), the sights will always be “looking at” a specific, fixed dimension above the bore of the rifle. But, as others here have pointed out, the path of the bullet is not a laser-like straight line. Exterior ballistics come into play. And for that reason, the sights must be adjusted to coincide with the trajectory of the bullet.
Keep in mind that when using any sights, they will be adjusted (for distances beyond the “close sight-in range” of 25 yards) to ensure a perfect bullet strike at only one distance. This is the point at which the sights align with the bullet path. Some folks refer to this as the point of convergence.
The offset is normally thought of in terms of having a 'scope mounted directly above the bore of the rifle. More interesting problems arise when the 'scope is mounted to the side of the rifle receiver, as in the M1 Garand and the older version of the Winchester Model 94.
Yes, I understand a certain amount of “hold over” or “hold under” is usually required. That’s why I said, “When you adjust the sights for a fixed target distance…” I was just trying to convey the concept that when you “adjust the sights,” you are adjusting the angle of the barrel, not the sights…