Where Does the Barrel Point When Round Fires?

[MachIVshooter]

Where does the rifle barrel point when it’s zeroed for some ammo at 200 yards at the time the bullet exits the barrel?

A couple of us already answered that for you. See posts #14 & #15.

Of your multiple choice options, many of us have told you "D) None of the above". It's a complex trig equation. You seem to be looking for an oversimplified answer, of which there isn't one; every single variable in zero range, firing angle and trajectory of specific load (including environmental factors) will alter the muzzle elevation angle.

 

[BCRider]

There's a bit of a trick to the question.

By asking about where the barrel is pointed AT THE MOMENT THE BULLET LEAVES THE MUZZLE you include a lot of the things related to recoil that can affect the answer.

All the concerns about gravity and bullet mass and the rest is similarly bundled into the wording "...equal to bullet drop at target range."

So in the end the bullet is going to drop over the distance by some amount which is already accounted for in the phrase "...equal to bullet drop at target range.". And added to that will need to be the extra distance it needs to rise to match the height of the sighting line above the bore axis.

So it's "B".

Yes the path is a curve and the barrel is straight. But the barrel is pointed upwards compared to the sighting system such that the bullet is started with an upward component so that the bullet will arrive at the sighted spot on the target "...equal to bullet drop at target range." That phrase from the question includes all the "stuff" that occurs during the ballistic trajectory as well as any upward kick in the rifle prior to the bullet leaving the barrel.

Sight height isn't irrelevant since the barrel is lower than the sight height and part of the setting of the sight is to make up for the height of the sights or scope above the barrel. And the external ballistics calculator over at the Hornady website that I've used for determining bullet drop also asks for the height of the sighting line because it does matter.

All in all it's a cleverly worded question. My first thought was also "D" but as I thought about what the phrase "...equal to bullet drop at target range." truly included I realized that the correct answer is "B".

 

[murf]

i voted "a". bullet drop is bullet drop no matter how high the barrel is pointed above the target.

murf

 

[danez71]

Is the point of aim at the 1st intersection of the trajectory or the 2nd?

 

[Bart B.]

Point of aim is at the target range; second place bullet crosses the line of sight.

Sight height used in virtually all ballistic software is the height above bore center at the muzzle where the line of sight is at. It's at zero range; the muzzle, where all exterior ballistics are calculated from. If the scope is 1.6 inch above bore center where it's mounted, the line of sight will be a little less above bore center at the muzzle because it has to be. If 20 MOA elevation's needed for a distant target and the muzzle is 20 inches away from a scope's front lens centered 1.6 inches above the bore, the LOS will be .111 inch lower or about 1.489 inch above the bore axis at the muzzle. Using the scope's actual height above bore center is close enough for most purposes. Measuring the front sight on iron sighted rifles for its height above bore center is also close enough for metallic sights.

 

[taliv]

i thought the use of 'zeroed' in the OP implied sight height was to be considered in the answer. that seemed consistent with the inclusion of sight height in some of the responses.

i think the answer is further complicated by the fact that the barrel is not fixed, but is in motion. the bullet exits the barrel moving on a vector that is not parallel with where the barrel is pointing, at that instant.

 

[BCRider]

But once the bullet breaks contact with the barrel, which is where this question starts, it's no longer has any upwards motion vector from the barrel movement.

It does get some additional rise angle due to the recoil but that's all taken into account by the sighting in procedure and that catch all phrase from the original wording.

 

[Bart B.]

You seem to be looking for an oversimplified answer, of which there isn't one; every single variable in zero range, firing angle and trajectory of specific load (including environmental factors) will alter the muzzle elevation angle.

'Tis my opinion that the answer is really simple regardless of every single variable in zero range, firing angle and trajectory of specific load including environmental factors. The answer will be the same for a different set of conditions as long as the conditions don't change while shooting a group of shots about the aiming point.

My prime objective in these questions is to see how people think about exterior ballistics. That's more important to me than what the correct answers are.

 

[DeepSouth]

I understand the reasoning my behind the question, but honestly the numbers are nearly unmeasurable (is that a word) after you figure in bullet drop. This is quiet literally splitting hairs. I've never really understood why people try to work out these "problems," it seems such a waste of time to me, but hey, different strokes for different folks I guess. Although, I will say it is sometimes interesting to read the different theories, I do learn from it.

 

[WardenWolf]

This is a loaded question, no pun intended. You're not even factoring in barrel vibrations and whipping that affect all guns to varying extent. Where it consistently hits tends to vary significantly from the static bore alignment at longer ranges; otherwise, boresighting would be far more effective that it is in practice.

 

[Bart B.]

It's not a loaded question, in my opinion.

I'm factoring in barrel vibrations and whipping that affect all guns to varying extent. Also factoring in the vibrations and other movements of what holds and aims the rifle, too, which add to that of the barrel.

While all the numbers for each contributor to barrel position are not precisely measurable, their total is easy to measure. This could be another question/poll. I've measured them several times.

 

[Sport45]

So what was the correct answer?

 

[Marty B]

What Llama Bob said!

 

[Nature Boy]

Where does the rifle barrel point when it’s zeroed for some ammo at 200 yards at the time the bullet exits the barrel

E. often not where it needed to be, based on the results of my groups

 

[Dr T]

For the record, I am in the D camp.

I have also observed that my 45 Colt with 7.5" barrel shoots light target loads several inches higher than full pressure loads at about 15 yards...

 

[Llama Bob]

What Llama Bob said!

It is interesting that after presenting an simple, easy to follow and indisputable proof of the correct answer, people persist in being wrong.

There is that old saw about leading horses to water...

 

[Bart B.]

Where does the rifle barrel point when it’s zeroed for some ammo at 200 yards at the time the bullet exits the barrel?

B. Above the aiming point equal to bullet drop at target range plus sight height above bore axis.

Here's why.

Let's take a bullet fired horizontally at 2700 fps that drops 10 inches below the line of fire (LOF) at 200 yards. The barrel has to point at a place on the target 10 inches higher for the bullet to strike where the barrel pointed.

With the rifle's sight axis (line of sight, LOS) 2 inches above the bore axis at the muzzle and parallel to the bore axis at the muzzle then fired horizontally, the bullet would strike 12 inches below the LOS point on the target. That's bullet drop plus sight height above bore axis.

In order for the bullet from that rifle and its sight to hit the point of aim 200 yards downrange, the LOS has to be aligned down about 6 MOA or 12 inches lower on target. When this is attained, the bore will still be horizontal but the LOS will be angled down about 6 MOA to intersect the target where the bullets strike. Bullets will first cross the LOS about 39 yards downrange and again at 200 yards.

If the rifle and ammo's zeroed for a 200 yard target at a 45 degree up angle, bullets will first cross the LOS at about 56 yards then strike at right angles to the LOF about 7 inches (sine of 45 degrees times horizontal 10 inch bullet drop) away from it. But the bullet still drops 10 inches in the vertical plane below the LOF.

 

[Llama Bob]

Where does the rifle barrel point when it’s zeroed for some ammo at 200 yards at the time the bullet exits the barrel?

B. Above the aiming point equal to bullet drop at target range plus sight height above bore axis.

Already proven to be false.

 

[Dr T]

At the end of the day, where the muzzle is actually pointed depends on a lot of factors. A fair number of them are random. This is summed up in

http://www.math.utah.edu/~cherk/hiawatha.html

 

[Haxby]

Not B or C.
Put a laser 1" under the barrel, a scope 1.5" above the bore, and put another scope on top of that one, 4" above the bore. Sight in at 200 with all three sights.
Then, it doesn't matter which line of sight you use. The barrel has to be pointed the same to hit the target.

 

[Llama Bob]

Not B or C.
Put a laser 1" under the barrel, a scope 1.5" above the bore, and put another scope on top of that one, 4" above the bore. Sight in at 200 with all three sights.
Then, it doesn't matter which line of sight you use. The barrel has to be pointed the same to hit the target.

Exactly. As previously stated, the sighting system is a red herring and doesn't factor into the problem at all. It could be any height you like, or removed entirely in favor of a simple level, and there would be no change in the answer.

 

[mainecoon]

In a safe direction.

 

[Tuxedo007]

That was my initial guess after some quick mathematical speculation.

Why speculate when you can calculate? (All calculations done at 4500 feet elevation and 29.95 corrected barometric pressure. 'Cause that's where I live.)

Using one of my favorite rounds, 8x57, with a 200 gr Nosler Partition going at 2500 fps. Scope height is 1.8 inches. (For sake of calculation, that's 1.8" above the bore at the muzzle). Assuming that the bullet crosses back over the line-of-sight at 200 yards from the muzzle.

Using values from jbmballistics.com.

Angle between line-of-bore and line-of-sight = 6.799 MOA or 0.1133 degrees.
Distance from muzzle where the line-of-sight and line-of-bore cross = 1.8" / sin(0.1133) = 859.6" or 23.88 yards.
Distance from that crossing to 200 yards = 176.12 yards or 63403.2"
Height of line-of-bore above line-of-sight @ 200 yards = 13.28"
Therefore, the line of bore is 13.28" above the bullet @ 200 yards. According to the ballistic calculator, that happens at 0.261 seconds into the flight of the bullet.

For comparison, let's move the sight height to zero and shoot the bullet straight out of a perfectly level bore. At 200 yards, the drop is 12.4" below the line of sight at the 0.261 seconds into the flight of the bullet.

Now, let's go back to the same angle, (6.799 MOA) but keep the sight height at zero. What happens? The bullet is 1.8" above the line of sight at 200 yards. Sounds familiar. That's the original sight height, which makes sense since we just adjusted it out for this thought experiment.

But, the original question was which of A, B, or C was the correct answer. (or none of the above)

Drop @ 200 yards from a flat barrel is 12.4". 12.4 + 1.8 = 14.2". The actual height above the line of sight is 13.28" in the original configuration, so the answer is D, none of the above.

I think.

Yes, I'm a math nerd. I buy math books (calculus, linear algebra, etc) at thrift stores because I like to. And who said you'd never use trig after getting out of school!?!?!

Matt

ETA: I had this typed up before I saw Bart B's addition of a specific load/velocity/etc.

This whole exercise is the reason ballistic tables exist! Or, one could hang or erect targets & very close intervals between the firing point & have a camera record the exact location of the elevation(in what ever units of measure you wish) of the muzzle when the bullet exits. Then, after careful gathering of targets & precise derivation of the elevation of the muzzle, you would then have the complete trajectory of THAT PARTICULAR BULLET from time it left the muzzle until it struck the target!

 

[Buck13]

Guns do not remain stationary while the bullet travels down the barrel!!!

For a barreled action cast inside a large block of cured concrete, the answer is A.

For a real rifle that we can pick up and handle, the answer depends on what you mean by "fired." I would take that to mean literally "the initiation of fire," i.e. when the priming compound increases significantly in temperature. (Alternately, you could take it as the break of the sear, but that introduces the effects of the shooter on the trigger and the rifle, which can be large, and the inertial motions of the hammer disturbing the rifle, which I suspect are not of interest to the OP.) As the bullet begins to move, this rifle begins to recoil, and since the bore axis is above both the rifle's center of mass and probably also above the center of resistance provided by the shooter's shoulder, the barrel begins to rotate upward, and the axis of the bore moves a great deal before the bullet exits. So, (ignoring barrel harmonics, which is a whole 'nother kettle of fish) in addition to its upward velocity due to bore inclination while sighting, the bullet velocity has an upward component to its motion due to the upward velocity of the muzzle rotating (roughly) around the butt stock, which I'll bet is small, AND an upward component due to the CHANGED inclination of the bore since the moment of firing, which should be larger. Neither of these can be easily determined, although I guess they could be approximated fairly well with enough computing power, but it's going to be a lot more calculating than you can fit on the back of an envelope!

So, the answer is D, since the barrel isn't pointed anywhere near where you think it was while aiming and firing when the bullet actually leaves the muzzle.

Somewhere in the Lee reloading manual, he alludes to this with an anecdote about a guy who was so proud of how much higher on the target his reloads hit than some other ammo. I can't remember how explicitly he stated this idea, but it seemed clear that he was implicitly pointing out that there are reasons other than "flat shooting" for your bullets hitting high on a target. At only 100 yards, slow, heavy bullets may hit higher than fast, light bullets from the same rifle and sight settings, because the barrel is inclined upward more when the bullet finally leaves the muzzle.

This is all very obvious when shooting revolvers at modest ranges with various bullets. Under 100 feet, trajectory is nearly insignificant. Light bullets, regardless of velocity, land low on the target. As bullet weight increases, the POI rises. Bullet weight has a greater effect on POI than velocity, with a magnitude of several inches at 25 yards over a 40% increase in bullet weight. My 4" half-lug GP100 .357 shoots 4 or 5 inches lower at 25 yards with 125 gr bullets than with 170 grain. Slow to fast loads at the same bullet weight have a much smaller effect: maybe an inch IIRC. (I say "revolvers" since the effect of moving slides, barrels and recoil springs makes this more complicated for automatic pistols. Sixguns are simpler, and I suppose also single-shot pistols, but I have little experience with those,)

tl;dr: Your gun is NOT stationary between the moment the hammer falls and when the bullet leaves the muzzle! The point you are aiming at is NOT the point the sights are aimed at when the bullet becomes a free projectile!