A Physics Lesson

['88Scrat]

Ok I need someone to explain something to me. This could be perceived as a dumb question...

Why when I take my SMLE No.4 MK1 and shoot with the 300 yard battle sight zero at 50 yards am I hitting a foot or more ABOVE the target? In my head I imagine this as two lines intersecting at a 45° angle at 300 yards (yeah I know thats an exaggerated example) with the top line representing the sight picture and the bottom line representing the travel of the bullet. Move the target forward and the top line, representing the sight picture, doesn't change but the point of impact should now be in the dirt right? I know bullets fly in a parabolic arc but could it really be that pronounced?

Man, not knowing this makes me feel kinda stupid...

[tangolima]

You are sure the battle sight has really been zeroed at 300 yards? And the ammo you were shooting, was it milsurp or close to the military load?

-TL

Sent from my SM-G930T using Tapatalk

[ms6852]

It has to do with your line of sight and the centerline of the bore of your rifle. Your line of sight is a straight line from zero to whatever distance your want... in this case 300 yds. The barrel of your rifle is actually aiming high but your line of sight is straight and the trajectory at 50 yds account for the 1 foot high impact so that when you aim at 300 yds your zero correlates with your line of sight. Check the link.

http://ffden-2.phys.uaf.edu/webproj/...tory%20(1).jpg

[JohnKSa]

It should be hitting high, but a foot at 50 yards seems too high. Are you sure it's actually zeroed at 300?

In my head I imagine this as two lines intersecting at a 45° angle at 300 yards (yeah I know thats an exaggerated example) with the top line representing the sight picture and the bottom line representing the travel of the bullet.

The sight line will be a straight line from your eye, through the sights to the target.

Because the bullet is going to be pulled down by gravity as soon as it leaves the bore, the sights are set to angle the barrel upwards slightly with respect to the sight line. That will lob the bullet upwards, above the sight line, on an arc that will allow gravity to bring it back down so that it coincides with the sightline at the zero distance.

So the bullet is going to start out a little below the sight line (since the bore is below the sights), rise above the sightline (probably somewhere around 25 yards from the muzzle) and keep arcing upwards until the point where it reaches the peak and starts to descend.

The peak of the trajectory will be more than halfway to the zero point. In a vacuum, the high point of the trajectory would be exactly halfway to the zero point--the trajectory would be a perfect parabola. But because of air resistance, the bullet is slowing as it goes downrange and the parabola gets skewed. The bullet has to be fired so that it will reach the high point after the halfway point to make everything work.

Anyway, after the trajectory peaks, from that point on, the bullet will be falling. It will fall until it comes back down to the sight line at the distance for which the sights have been zeroed. It will keep falling, faster and faster the farther it goes downrange since the acceleration of gravity is constant and constant acceleration means constantly increasing speed.

This website has a good picture showing the relationship of the sights and the bore.
http://www.mainviewtech.com/en/branded.php?pid=193

['88Scrat]

So it is the arc of the bullet I wasn't taking into consideration...

As far as the sights on my rifle, they are the standard battle sights found on the SMLE No.4 MK 1 and everything I have read says the BSZ should be 300.

[T. O'Heir]

A No.4 MK1 Lee-Enfield is not an SMLE. Only a No. 1 MK III is an SMLE.
"...perceived as a dumb question..." No such thing.
"...the 300 yard battle sight..." Is about Mk VIII ammo with its 174 grain bullet at 2440 FPS. Pretty much, only. It also has to do with the height of the front sight blade and where you're holding on the target.
Anyway, at 50 yards the bullet is still rising on its trajectory arc.
Read this.
https://www.milsurps.com/enfield.php?pg=ti15.htm

[Jim Watson]

Tim Mullin wrote that there are untold thousands of people born to soldiers whose enemies could not hit them at 50 yards with rifles that would not zero closer than 300.
Applying mostly to the generation whose Fathers fought in WWI.

[mehavey]

[JohnKSa]

.303 ballistics aren't as good as the .30-06, but the graph is still instructive. I can see being a foot high (maybe even a little more) for the .303 at midrange. But being a foot high at 50 yards seems wrong.

I would expect something more like 6-7" high at 50 yards.

[jimbob86]

.303 ballistics aren't as good as the .30-06,

What bullet is that in the chart? Lyman Lead Somthin' What Gas Check? If it is this bullet-

http://www.westernbullet.com/ly3gr1.html

Looks to be as aerodymanic as a greyhound bus with all the windows open.....


...... I'd imagine a 174gr .303" spitzer or spitzer boat tail would be flatter, even if only pushed to 2540 ft/ sec....... that was the WWII loadings (Mk VII and Mk VIII).


Somebody with a ballistics calculator run the numbers, please......

[mehavey]

Actually, when I went back and re-did the calcs for the standard Mark-VII loading (above),
the 303 very closely approached the 175 SMK 7.62 NATO sniper/match round...
about ±8" all the way out to 350. Really doggone good in fact.

That post somehow "disappeared"

[jimbob86]

Mehavey, the closest Lyman bullet I could find with a listed BC was LYM LFN GC 311441 .... sounds close ..... BC listed was .143 ..... no wonder the graph seemed so steep (that and I am used to figuring flight paths for .270WIN .....

[mehavey]

so it was...
(see lower left corner of chart)





(it has a nose only Victor McLaglen could love)

[jimbob86]

LFN was Lead Flat Nose ..... LBN? Lead Blunt Nose?

[mehavey]

See
https://www.google.com/search?biw=15...dP8KjBIehrCqM:

[Jim Watson]

We don't know that the OP's 300 yard sight setting is actually on target at 300, do we?

[JohnKSa]

What bullet is that in the chart? Lyman Lead Somthin' What Gas Check?

Yup, I should have paid more attention. You never know when someone's going to post a trajectory for a gas-checked lead bullet in a thread about the .303.

At any rate, that makes a foot high at 50 yards even more improbable. Sounds like the sights aren't really zeroed for 300.

[mehavey]

Heck, I'm running GCs in my own 303, 30-40, 308, 30-06, 375H&H ... aaaaaand
at numbers starting with "2".... (hence the leftover bullet in QuickTarget)

Looked quite normal in passing glance.

['88Scrat]

I'll take another look at the sights. There don't appear to be any obvious modifications to them. Anything in particular I should look for?

[jimbob86]

If the rear sight looks unmodified/ undamaged ....check the front sight.

[TRX]

Unless you know *which* .303 British ammunition your sight graduations are for, you're out of luck.

Over the years the Brits changed the bullet weight and velocity of the .303 several times. The trajectories varied quite a bit.

As for SAAMI or CIP spec hunting ammo... who knows.

[James K]

It should be recognized that for long range shooting the bullet will cross the line of sight twice, once on the way up and again on the way down. At the latter point, if the rifle is sighted in properly, the bullet may impact the target and stop or continue past/through the target. This is taken advantage of in military training where it allows rifles to be sighted in at short range and retain the same sight setting at hundreds of yards.

Jim

[badbot]

My 308 starts about 2.6 inches below line of sight crossing los at about 50y the arc peaks 6 inches above los then drops crossing los at about 330y and ends up 6 inches low at 500yards.
so I am within 6 inches of los from the muzzle to 500 yards.
so aim center mass and rock and roll
No guess work until well after 500y then hold over

[Jim Watson]

Which is the logic behind the 1903 Springfield Battle Sight, a center hold on a man would hit him somewhere out to 500 meters, 547 yards.