bullets settling down?

[unclebill]

i always thought bullets settling down in flight sounded like a bunch of hooey
but now i aint so sure
my 300 meter groups are smaller than my 100m ones
same ammo/conditions/gun
but i am having a hard time wrapping my head around it.
ok
somebody whip out that big brain!

[country gent]

Scope or iron sigh? Another reason for this is the human eye can discern a certain amount of error and this stays about the same wether 100 yds or 300yds. AN example is you can see with in the same sight alighnment of .010 ( example chosen at random) both alighnment and on the target, at 100 m this is much more error than the same at 300 yds. Also some long for twist do take longer to fully go to sleep. I shot 6mm 115 grn vlds from a 243 in NRA High power for 600 -1000 yds. testing at 200 yds was hard as thesee wouldnt be asleep yet.

[Ballistics in Scotland]

i always thought bullets settling down in flight sounded like a bunch of hooey
but now i aint so sure
my 300 meter groups are smaller than my 100m ones
same ammo/conditions/gun
but i am having a hard time wrapping my head around it.
ok
somebody whip out that big brain!

Don't give up now, I'm sure you will be better off if we leave it where it is.

It would be interesting to know just how they are bad. Are they strung out up and down, or in all directions? In that case it could be due to compensation, the phenomenon for which the SMLE, the First World War short Lee-Enfield was famous. It had a rather thin barrel which was liable to flip weak rounds high, but powerful rounds lower. At 100 yards the groups with bad ammunition could be quite dreadful, and yet they could be good at 800 or 1000. At Bisley in England the main event for many years used a common issue of military ammunition. Mausers or the P14 Enfield tended to give superior accuracy at any range when the issue was good, and all the time at 200 or 300. But for long range when the ammunition was inconsistent, the Lee-Enfields came into their own.

If the group starts well and then shifts as the rifle warms up, I would suspect bedding of the barrel or action. That ought to affect 100 and 300 yards equally, but as you can't do both at once, maybe it was hotter for one than the other.

Then there is a test which is rather tricky to do. When you shoot at 300, it should be possible to set up a piece of thin paper at about 150 to 180 yards, so that bullets will pass through it while you see under it to the aiming point. The idea is to see whether the bullets are keeping to the same place in the group, left-hand at 180 being left-hand at 300. If they are curling around one another in air spirals, so that the left-hand bullet may be left-hand at 300, you have established virtually for certain that it is a bullet rather than a rifle or charge problem.

Imagine if the centre of mass of your bullet is a thousandth of an inch off-center - and the performance of some benchrest bullets prove for certain that they are many times better than that. As the bullet proceeds down the bore, the weight of the bullet is, in effect, moving in a spiral of .002in. in diameter, or about .006284in. diameter.

But Newton's First Law of Motion says that a body will either remain at rest (not applicable here) or move in a straight line and at a constant velocity, unless it is acted upon, unless it is acted upon by an external force. As soon as the rlfling stops exerting its rotational force, that straight line is going to be the direction in which the bore spiral was pointing at the time. The angle it makes with the bore axis is the same as it would in travelling from one corner to another of a rectangle with length equal to the rifling twist, and width .006284in.

That doesn't sound much of an angle, but if the twist is 10in., your bullet will be 3600 times .00684in. off at 1000 yards, or 24.624in. A 45.248in. group at that distance mightn't sound like disaster, but it is in addition to all other sources of inaccuracy. Clearly the bullets we can buy are pretty good. Since this source of error is exactly proportional to range, and doesn't settle down, your rifle is exonerated from this kind. You can even fake it, by drilling tiny holes into the bearing surface of the bullet, positioning them at 12, 3, 6 and 9 o'clock in the chamber, and make four different, but perhaps good, groups on the target.

But imagine that eccentrically weighted bullet with the outside revolving around it. The tendency is for it to rotate around the centre of mass. This is like a tiny rudder, steering it into a completely different spiral, the air spiral. This is the one that in bad cases can intensify until the bullet tumbles of breaks up, or may settle down somewhat. The best way to test if this is the problem and is curable, is to substitute different bullets which you know to work well for other people.

The only ways I can think of that a bullet problem isn't made or bought with the bullet are bad crowning of the barrel, which can induce a wobble, or melting of the core, which may leak out asymmetrically. The test for this is to fire through a paper sheet set up at about fifteen yards from the bullet (earlier is before it leaks out, and further is after it has stopped), and see if spiral trails of melted lead become visible on the paper. The will look a bit like photographs of galaxies in space, which are also created by centrifugal force.

[MtGun44]

Yes, bullets settle down after flying a while.

Hatcher discovered that when they tested a range structure design (thick oak boards) to
see if a .30-06 would penetrate, it would not. But later, reports in the field were that
the boards there, apparently identical, were being penetrated by the same ammo.

The difference? Several hundred yards farther from the muzzle the bullet is settled down
and stable and penetrated much farther in hard wood than the same ammo at 15 ft range,
bullet hadn't yet settled down and would tumble in the wood, limiting penetration.

Real phenomenon.

[leftiye]

Many instances of what you observed. My .375 H&H Improved shoots finer at 200 than at 100 yds. I believe McMillan had same experience with .50 Browning sniper rifles. .44Man can see it happen. The bullet spirals around trajectory line and then settles down.

[Tatume]

This phenomenon can usually be attributed to parallax. High powered scopes are adjusted to neutral parallax at longer ranges. When shooting at close range the position of the shooters eye causes errors in sighting. If you teach yourself to center your eye in the scope, your 100 yard groups will improve.

The argument about bullets being off course and then finding their way back will go on for centuries.

[Ballistics in Scotland]

It can be observed with target aperture sights. Dr. Franklin Mann documented it in 1904, in what is still one of the best books on exterior ballistics in hand firearms, with test barrels set in a cast-iron V-rest, when the shots weren't individually aimed at all.