Thread: Accuracy at 100 vs 600 (example). Variations in accuracy at different ranges

My copy of 'The Sharp Shooter' explains it as all the bullets in a group actually spiralling in the same direction as the twist of the bore (x spiral) then due air pressure building on the tip of the bullets, because they are not flying completely in line with the direction of travel. This air rolling off on the opposite side to the x spiral initiating a y spiral.

So what this means is that bullets move away from the line of sight then move back and cross it and then disperse outwards again then straighten out of these spirals again but not before they have taken their dispersive effect.
To Quote Matt and Bruce Grant: 'The occasional extraordinarily good group which shooters preserve and show off is due to y error for the shots all combining within the circle of x error at the target. Ironically, a group from the same shots taken at almost any other range would show a wider dispersion'.
What I take this to mean is that a target shooter would need to have a box of ammo tuned for each range that they will shoot at.

A link to the original work of DR FW Mann https://duienforcers.wildapricot.org...unnCo_1909.pdf

'.

Originally Posted by ChrisW

Its not possible. A projectile cannot just alter its course mid flight (other than due to external factors, wind etc), as would be required in order for a projectile that was shooting say 1 inch at 100 to shoot better than that at distance.

In theory absolutely correct.
Practical, no projectile is 100% eccentric which means right at the start, when the centrifugal forces are high, the projectile yaws - and depending how bad it is, changes the course of flight. Later in it's flight, friction slows down spin and speed of the projectile which results in less centrifugal force so the projectile does settle down and it's impact becomes more predictable (better groups). Even later in flight, the spin is no longer high enough and the projectile starts tumbling - which again can change the course of flight. The US Artillery has a book which describes these effects on shells and projectiles and how to calculate it...

I thought the reduction of spinning is way smaller than the reduction of speed of the projectile , therefore more stable as speed decrease.
? ( provided it was launched with a fast enough spin at the beginning to remain stable ,all the way to and sometimes through the speed of sound and beyond)

The theory of the fast projectile going a bit lower and the slow projectiles being thrown a bit higher is the theory used with the barrel tuners I believe

Originally Posted by Friwi

I thought the reduction of spinning is way smaller than the reduction of speed of the projectile , therefore more stable as speed decrease.
? ( provided it was launched with a fast enough spin at the beginning to remain stable ,all the way to and sometimes through the speed of sound and beyond)

The theory of the fast projectile going a bit lower and the slow projectiles being thrown a bit higher is the theory used with the barrel tuners I believe

My understanding of the lighter lower / heavier higher was as the barrel lifts in angle with recoil, the lighter bullet is out of the muzzle faster and the heavier one is in the barrel fractionally longer and recoil lift is the cause.

Now myy acceleration maths is a bit rusty , but if a load will send a lighter projectile in my 308 out at 2900 fps at the muzzle and the heavier one is out at 2650 fps then time in the barrel is average speed x length of barrel.

EG 24 inch barrel. Ave speed is about for each is 1450fps for the fast one and 1325 fps for the slow one. so the fast one will spend 1.38 milli seconds in the barrel (1.38 thousandths of a second) and the slower one 1.51 milliseconds. A difference of about 9% (IE 9% longer in the barrel as it is lifting....)

Originally Posted by stagstalker

I have heard of the term where a projectile or load settles down at distance and gets accurate where as it might not look that flash at say 100metres on paper. I have also heard the opposite, a nice group at 100 but opens up at distance and turns to rubbish. What is people’s experience with this?

My current 284 load seems to be the first example. It doesn’t do much flash at 100 but when I was shooting the gong at 575 yards it was shooting like a tack driver. I always thought it didn’t make sense?

The answer is in your question, you were shooting for "groups" at 100 and "hits" at 575 yards.

Originally Posted by Max Headroom

I have found that aiming at a smaller target at 100 gives a smaller grouping than aiming at a large one.

So aiming at the same size target at 100m as at 200m forces the fine aiming to be more precise due to the perceived reduced target size.

More about the aiming process than the physics which remain constant.

Same principle in the teaching of "point shooting" with a pistol. If you "point aim" centre mass of a human target you apparently make less tight groups than if you aim at, say, a shirt pocket. I won't go out and test it though.

Originally Posted by Moa Hunter

My copy of 'The Sharp Shooter' explains it as all the bullets in a group actually spiralling in the same direction as the twist of the bore (x spiral) then due air pressure building on the tip of the bullets, because they are not flying completely in line with the direction of travel. This air rolling off on the opposite side to the x spiral initiating a y spiral.

So what this means is that bullets move away from the line of sight then move back and cross it and then disperse outwards again then straighten out of these spirals again but not before they have taken their dispersive effect.
To Quote Matt and Bruce Grant: 'The occasional extraordinarily good group which shooters preserve and show off is due to y error for the shots all combining within the circle of x error at the target. Ironically, a group from the same shots taken at almost any other range would show a wider dispersion'.
What I take this to mean is that a target shooter would need to have a box of ammo tuned for each range that they will shoot at.

A link to the original work of DR FW Mann https://duienforcers.wildapricot.org...unnCo_1909.pdf

'.

To clarify, as explained by Grant, bullets enter the rifling non-concentric with the bore and rifling (concentricity is only an approximation, 100% concentricity is a mathematical concept, not practically achievable).
This leads to bullet WOBBLE as they are spun by the rifling, which in turn leads to a CORKSCREW, flight path.
Eventually centrifugal and aerodynamic forces cause the bullet to stop wobbling, and it flies straight from there on.... but from a random point in the spiral. Grant stated that rifle shooting targets, if enough shots are fired, show up a donut pattern of impacts for this reason.

So from this, yes, bullets fly straighter paths after the first 100 - 140 yards, but they are thrown off aim before that. The initial wobbly/corkscrew flight must have quite an energy cost too.

Originally Posted by JaSa

In theory absolutely correct.
Practical, no projectile is 100% eccentric which means right at the start, when the centrifugal forces are high, the projectile yaws - and depending how bad it is, changes the course of flight. Later in it's flight, friction slows down spin and speed of the projectile which results in less centrifugal force so the projectile does settle down and it's impact becomes more predictable (better groups). Even later in flight, the spin is no longer high enough and the projectile starts tumbling - which again can change the course of flight. The US Artillery has a book which describes these effects on shells and projectiles and how to calculate it...

Yes the military are the ones who really know this stuff and how to predict it. So in essence, a group that is dead on at 100 might strike left or right at 600. I understand it that if someone wants a dedicated 5-600 metre load, then the load should be developed at that range

I'd be thinking more about my technique than looking to the rifle etc for answers.

To "read" groups you need to be doing several of them, and seeking consistency - a modern rifle that will shoot well at 500 yards/metres will be shooting well at 300, 200 and 100, ask any F Class shooter.

I see many small groups shot at various ranges, but they are usually "cherry picked", and the shooter isn't aware that they are doing it (to themselves). If I had a $ for every time I'd heard someone say "oh I pulled that one" I'd be rich - but usually the only person they are kidding is themselves, their group just opened up and it was the rifle/ammo.

Someone will no doubt say that "I shoot well on game but can't shoot groups" and many people can knock over animals without being a particularly good shot - an animal has a pretty large target area. If you think you are getting good then try head shooting rabbits at extended ranges from various positions.

There are those who are good on a range but struggle to make shots in the field outside of the controlled terrain and position of the range.

However If you look at the guys who win at the likes of Sparrowhawk and Jungle Lane type shoots you'll find they can shoot well in all scenarios and their groups at closer ranges will be itty bitty things.

Artillery have a few extra things to consider as well amongst them there's barometric pressure, wind direction and speed at varying altitude, compass bearing, latitude and rotation of the earth during time of flight.
Some of these may start to have an influence for rifle shooters at extreme long range wind certainly does even up close

Originally Posted by Tentman

many people can knock over animals without being a particularly good shot - an animal has a pretty large target area..

Consistently hitting minute of deer is a pretty good standard to start with, but to develop beyond this is a better thing.

(Having said minute of deer, I mean the vital kill shot parts, not the whole beast)

Originally Posted by grandpamac

Greetings All,
There are a couple of things that can result in apparent better accuracy at longer ranges. Note the word apparent. The first is scope parallax. Non parallax adjustable scopes are set to be parallax free at 150 metres or more. This can result in slightly larger groups at 100 metres than 150 to 200 metres in MoA. The rifle is not more accurate at the longer range, it's just better aimed. For longer range with the .303 target rifles the reason is a little different. Talking to some of the older target shooters who had used the No 4 Lee Enfields they believed that the rifles tended to throw faster projectiles a little low and slower ones a little high. The ammunition they were using was military and velocity varied somewhat so the rifles compensated (their words) and brought the fliers closer to the centre at longer range. All but one of the rifles I have had over the years strung the shots up the target as velocity increases, some much more than others. The exception was a Winchester 88 in .308 which strung them in the other direction. Never tried it at 900 yards though.
Regards Grandpamac

This pretty well nails the two known causes of better grouping at longer ranges:
parallax not set correctly for short range (also sometimes target or reticle focus)
"compensation" IF barrel flip is opposite to velocity variation. Only recognised for SMLE. Will give a group compressed in the vertical dimension, which fullbore target shooters use as their measure of grouping due wind unpredictably spreading horizontal dispersion.

Vastly more common is that the group diameter increases exponentially at longer ranges due to poorly stabilised bullets. Depending on the rifle and projectile, this can be from 200m (my .303 with 125gr) to 500m (my 7m08). The best example I have is my 22, which gives sub MOA groups with most ammo at 25 yd (several brands around 0.5 MOA), but only RWS50 and Eley Tenex were on 1MOA at 50m and Eley match was 1.5. This also showed that, for 22LR ammo, quality affected this loss of grouping at longer ranges. Past a certain distance, the bullets don't even register on target - its as if they vapourise. My standard 7mm08 load shoots 0.3 mRad at 100m, 200m and 300m but struggled to ever hit a 1mRad target at 1000 m (gone subsonic too).

The reason for doing load development at longer ranges is mostly because that is where velocity variations due powder measurement, neck tension and jump have an effect on point of impact. "ES" doesn't affect grouping at 200m but it is key at 1000m. Presumably bullet stability problems due to reloading errors like concentricity and projectile quality, length, shape, spin rate are also more easily detected at longer ranges too.

vital area of a red deer is similar in size n shape to a 3ltr plastic milk bottle......just about anyone can hit one of then broadside on at 100 yards...turn it end on and the size deminishes by about 70%...still relatively easy to hit but you can bet your last dry pair of socks you will be aiming a lot more carefully. now rotate that jug around so you can see the lovely round blue (not green thats "lesbian milk") plastic lid......now in theory any of you folk who claim to be shooting sub moa shoould be able to poke a hole in guts of the lid piece of piss,after all they are 1 1/2" across...shite you lot should be able to shoot that out to 200 yards all day long with your 3/4 moa rifles......... whats this got to do with discussion?????
go make yourself a cuppa tea and have a good look at that lid......its plurry small really,if you were to aim at it at any distance over say 150 yards you would HAVE to have your technique 100% spot on to hold cross hairs inside that wee plastic circle long enough to squeeze off a shot....at 100yards not so much.

a wise man once said that when sighting in you need to be realistic,if you having an off day and think you are wobbling around like titties on a trampoline,crosshairs moving 2-3" around centre of bull....well you are more than likely to only manage a 2-3" group at best....
if however you are rock solid and can close eyes for 10 secounds and open them to be still on target,you are likely to shoot as good as rifle can..
heck I dont even shoot out past 350 so what would I know.

I’d say if you are wobbling around 2 - 3” on target at 100 then you need to re asses your position, support and alignment etc for yourself and the rifle. A good stable setup should have you pretty damn steady before you’re even starting to think about squeezing off a good shot. This is in the context of doing a zero or shooting for a good group / testing ammo of course.

agreed.....the point I was trying to make is that the rifle can only shoot as good as you make it.....a really gusty or howling windy day is another...its the only day you have to sight in before going away....if you calling your "wobbles 2" and you get a 2" group close to where it should be....well chances are you will be fine.
many many rifles are checked over bonnet of car at a inch thick cross drawn on bum of pizza box ...hardly the ideal set up and to expect sub moa is pushing it a bit.
make the cross 1/4" thick and go into damped prone at least and results will be far better.
one of the tightest groups I have ever shot with my old poohseventy was checking sights at 200 yards on deerstalkers range at pleasant point...only had a hundred yard target and a 4x scope....damped prone over a bed roll and surprised the heck out of myself with 3/4".........one of those fluke groups mentioned earlier,combined with having to really concentrate hard on centring target.