Serious Rifle Operators Avoid The Back Curve
BY Herschel Smith
6 years, 3 months ago
The bullet then continues to rise until, under the influence of gravity, it starts to fall back toward the sight-line. This highest point in the bullet’s flight, the “maximum ordinate,” is reached at 140m. At this range, the bullet is six centimeters above the sight line, but no more.
As it continues downrange, the bullet then falls back toward the sight-line, crossing it once more (this time on the way down) at 240m. This is the “second intersection.”
The bullet then continues to fall until it is, once again, six centimeters below the sight-line. This takes place at 260m.
So, between point-blank and 260m, the bullet is never more than six centimeters away from the sight-line, “all other things being equal.”
However, the foregoing holds true only when the rifle itself, as it is fired, is perfectly horizontal. When a shooting position necessitates the rifle be fired from a “rotated” position, the six-centimeter standard collapses after 150m.
Thus, I tell students that their M4 is basically a 150m gun. Within that range, it is deadly accurate, no matter the shooting position, no matter the wind, no matter most other factors.
The “back-curve zone” is that portion of the trajectory which lies between maximum point-blank range and the ultimate point of bullet impact. Any time a rifleman is working in ranges that involve the “back-curve” of the trajectory, that is, after the bullet has fallen more than six centimeters below the sight line (after the second intersection), the path of the bullet becomes harder and harder to predict.
[ … ]
Yet, today’s snipers are amazing is (sic) their ability to skillfully use the back-curve zone, and they enjoy my admiration! But, the rest of us, under “field conditions,” using generic military rifles, will squander much ammunition trying (mostly in vain) to get reliable hits there.
Well then. I need to tell my former Marine that all that 500 yards qualification he did to earn the expert rifleman badge is worthless. And all of those kills he had at greater than 150 were just fake news.
Who knew?
On January 1, 2018 at 1:26 am, DAN III said:
Mr. Smith,
Gee, you attribute the quoted remarks to “Ammoland” when they are in fact an extract from an essay by noted firearms trainer John Farnam.
You must have mistakenly omitted Mr. Farnam as the author.
On January 1, 2018 at 1:40 am, Herschel Smith said:
Matters not to me to whom the quote should be attributed.
On January 1, 2018 at 2:16 am, DAN III said:
Mr. Smith,
The Ammoland piece was specifically authored by John Farnam. Yet you choose to ignore making proper attribution. Why not attribute the quote to the actual author ?
“Matters not to me whom the quote should be attributed.” It should. You do a disservice to those who read your blog and expect integrity. Instead, you contribute to the “fake news” meme so prevalent today in the blogosphere. Sad.
But hey….it is your blog. Happy New Year.
On January 1, 2018 at 8:40 am, WiscoDave said:
If you access the link it goes directly to AMMOLAND.
There, right below the article title you see “by John Farnam.”
I have never seen any linked article, on any website, that attributed the author of the piece in the link to the piece.
It is indeed Mr. Smith’s blog but, in fact, he is doing nothing different than any other “blogger” out there.
On January 1, 2018 at 9:41 am, Herschel Smith said:
@Dan,
I didn’t so much “choose” to do anything at all except link an essay. It’s customary to cite a web site, and then it’s also customary to cite the author’s name. Most often if I am intending to discuss a specific author who I know has said something of interest to me in the past where I also intend to draw parallels to said essay in the past, I’ll mention a name. Otherwise, it’s also common practice to cite the web site.
I’m not sure why this is important to you. The commentary could have been written by Donald Duck for all I care. I don’t know the man, don’t care about him, and as far as I’m concerned, I could also shout it from the rooftop.
The commentary was written by John Farnam. It was written by John Farnam.
John Farnam.
JOHN FARNAM.
JOHN FARNAM, dammit.
I hope that clears things up.
The commentary was apparently written by John Farnam.
On January 1, 2018 at 9:43 am, Herschel Smith said:
This is awesome. Now I’ve got something else in my life I have to worry about. How to I cite articles and will my readers think I secretly intended some slight if I didn’t cite the web site or author, or both?
Oh brother.
On January 1, 2018 at 12:44 pm, Ned said:
Thankfully, I’ve never been a “serious rifle operator.” Otherwise, I wouldn’t have shot so many deer and elk over 150 meters.
However, like many other readers, I will now dutifully comply with these instructions for actual serious rifle operators.
Now, when do I get my serious rifle operator badge?
On January 1, 2018 at 6:47 pm, WiscoDave said:
Herschel, please do not think that my comment was directed at you in any way. It was intended to point out to DAN that he was incorrect and wrong in his commentsry.
If you thought I gave offense I apoligize.
On January 1, 2018 at 7:45 pm, Herschel Smith said:
@WiscoDave,
Oh absolutely not.
On January 1, 2018 at 11:23 pm, Backwoods Engineer said:
“The bullet then continues to rise until, under the influence of gravity, it starts to fall back toward the sight-line.” I wish people would stop talking about bullet “rise.” This is only the apparent trajectory. The bullet actually falls from the moment it leaves the barrel, but because of the orientation of the boresight to the slightline and to the perpendicular of the earth’s gravity vector , we have apparent rise. The bullet never actually goes any higher than the barrel.
On January 2, 2018 at 2:33 am, Jorge said:
Despite the fact that the AR was built to permit shots on target from 0-300 with no sight adjustment so your minimally trained draftees could make hits out to typical engagement range, we will limit it to M1 Carbine ranges for ‘serious operators’? In an era where ACOGs are ubiquitous in infantry units, and good variable optics are quite inexpensive, we will stick to PDW distances?
On January 3, 2018 at 12:19 am, Georgiaboy61 said:
Hey, I know that I am only a knuckle-dragging redneck from south of the Mason-Dixon line, but don’t “all” shooters serious about mastering their firearm – rifle, pistol, shotgun, whatever it may be – know that they must also master the characteristics of the loads it fires and its trajectory from start to finish?
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Re: “This is only the apparent trajectory. The bullet actually falls from the moment it leaves the barrel, but because of the orientation of the boresight to the slightline and to the perpendicular of the earth’s gravity vector , we have apparent rise. The bullet never actually goes any higher than the barrel.”
Backwoods Engineer, your statement is entirely correct until the last sentence, “The bullet never actually goes any higher than the barrel.”
Gravity begins acting on the projectile (bullet) the moment it exits the barrel, at 9.8 meters per second per second (the acceleration due to gravity). If the rifle barrel is close to horizontal and nearly matched the line of sight, then your statement would largely be true. However, if the shot is of any serious distance, the barrel must be aimed in a much higher arc – and no longer resembles a straight line of sight.
Consider a .308 Winchester 175-grain Sierra Match King BTHP being fired at 2600 fps from a bolt-action rifle (22″ barrel, 1:11 RHT) with a scope zeroed for 500 yards. The near-zero is inside of 25 yards, whereas the far-zero is at 500 yards, with the bullet reaching a height of 21.9 inches above the LOS at 275 yards before heading back down to the 500 yard far-zero point of intersection. By the time the shot reaches 1000 yards, it has – according to my Sierra ballistics software – a trajectory of 277 inches of elevation, or about 23 feet.
That’s a serious parabolic arc, one which sees the projectile rise well above the barrel at its maximum ordinate. The environmental conditions are for my area, which is 880 feet above sea level. The trajectory data may vary where you are, but not substantially-enough to change the conclusion, I do not believe.
If my calculations are in error, please be so kind as to explain how. Thanks for posting…
On January 3, 2018 at 12:26 am, Georgiaboy61 said:
Re: “If my calculations are in error, please be so kind as to explain how.”
BWE, in proofreading my work, I discovered an error before you had a chance to do so.
The particular rifle set-up mentioned features a 500-yard zero (equivalent to POI 11.75 inches above POA at 100 yards), but obviously, the max. ordinate for a 1,000 yard shot would occur much further out than 275 yards. If my calculations are correct, the max ordinate of a 1000-yard shot would occur at 575 yards, at about 141 inches – or 11.75 feet above the LOS.
My apologies for any errors….
On January 3, 2018 at 12:58 am, Georgiaboy61 said:
“serious rifle operators avoid the back curve”
Maybe all of your former military types can explain this, then…
Isn’t firing a .50-cal Browning HBMG out to long range to interdict enemy troops on the reverse slope of a hill using the “back curve”?
What about plunging fire weapons – such as mortars or howitzers – capable of dropping rounds on enemy troops or hard targets behind an obstacle? Aren’t those weapons and their operators using the “back curve” or downward portion of the trajectory of their shots, to their advantage?
In naval gunfire engagements between capital ships, or when a battleship or heavy cruiser fires its main batteries at shore targets, anything two-three miles or less is considered point-blank range.
The Battle of Savo Island in 1942 between the northern coast of Guadalcanal and Florida Island on the night of August 8, 1942, was such an engagement; ships often fired over open sights as distances were so short in the confined spaces of the New Georgia Sound off Savo Island. The main guns of the capital ships were direct-fire weapons for the most part.
On the other hand, as the ranges lengthen to 10-15 miles or more, the targets are usually not visible via line of sight due to the curvature of the earth. In these instances, the main batteries are not line-of-sight, direct-fire weapons, but indirect fire weapons dependent upon plunging fire for their effects on target.
The Battle of the Denmark Straits, fought upon the seas between Iceland and Greenland on 24 May, 1941, which saw the German battleship Bismarck sink the battle cruiser HMS Hood – was fought at ranges up to fifteen miles. The Hood opened fired at the lead ship in the German column, believing it to be Bismarck when it was actually the heavy cruiser Prinz Eugen. The later salvo by Bismarck that ultimately destroyed Hood in the catastrophic explosion of her ammunition magazines, was fired at a range of eight miles. The steep trajectory of the Bismarck’s 15-inch shell fire was instrumental in the dramatic destruction of the Hood, whose decks were inadequately armored against plunging fire, a design concession made in the interests of saving weight.
Only three crewmen from the HMS Hood survived the sinking. The last of these, Ordinary Signalman Ted Briggs, died in 2008 at the age of 85.