shot grouping

[awadhnavab]

As a new shooter I would like to ask.....what is the most likely cause of shooting moderately good groups on different targets on the same session but each group is very differently placed....one group on one target would centre around 3 o'clock at the nine ring, for example, while another would centre in some other quadrant of the target. Since this change is usually after a change in the target, I would presume it is because of change in grip? Am I "on target" !

[Fred Mannis]

As a new shooter I would like to ask.....what is the most likely cause of shooting moderately good groups on different targets on the same session but each group is very differently placed....one group on one target would centre around 3 o'clock at the nine ring, for example, while another would centre in some other quadrant of the target. Since this change is usually after a change in the target, I would presume it is because of change in grip? Am I "on target" !

This is not unusual and could be due to:
- change in grip
- change in npa
- change in muscle tension from walking around to change the target.

Do you check grip for proper natural sight alignment and your stance for npa when you resume shooting? Some stretching exercises before you start and between target changes may be in order.

[alb]

It may be simply a function of probability. It depends on how many shots you shoot in a group. For example, if you shoot 5-shot groups, both the size and the center of the groups will vary widely, particularly if you are a new shooter.

However, if you were to shoot 50-shot groups and drop the worst 5 percent of your shots from each group, you would find that both the size and the center of the groups would be a whole lot more consistent. The size of such groups would also be a much more accurate indication of your level of skill.

Regards,

Al B.

[Richard H]

It may be simply a function of probability. It depends on how many shots you shoot in a group. For example, if you shoot 5-shot groups, both the size and the center of the groups will vary widely, particularly if you are a new shooter.

However, if you were to shoot 50-shot groups and drop the worst 5 percent of your shots from each group, you would find that both the size and the center of the groups would be a whole lot more consistent. The size of such groups would also be a much more accurate indication of your level of skill.

Regards,

Al B.

Its called the Central Limit Theorem. His question still holds as he wants to know what causes his grouping.

[EdStevens]

I get the same thing. Essentially it means I'm doing the same thing wrong, consistently. Sometimes it is a physical cause (NPA, trigger finger placement, etc.) but very often it's mental. A little anticipation of the shot that causes a micro-twitch of the muscles coming from the subconscious that is very consistent during a string or even several strings and creates a decent group in the wrong spot. Calm confidence, smoothing out my trigger pressure and concentrating on the front sight can usually bring the shots back into the centre.

[alb]

Its called the Central Limit Theorem. His question still holds as he wants to know what causes his grouping.

Actually, the phenomenon I was referring to is known as 'Poisson clumping'.

Before we can adequately determine what is causing changes in the center of his groups, we need to understand what he means by a 'group'. Fred Mannis listed a number of things that might affect the location of the center of a group. But, he left out 'arc-of-movement'.

When you shoot a group, the center of the group is always going to be somewhere. For groups with a small number of shots, the center of the group can change significantly, particularly if you have a large arc-of-movement, which presumeably the original shooter has, since he identified himself as a new shooter.

Top shooters have a small arc-of-movement, and their shots all tend to fall randomly within it. New shooters have a much larger arc-of-movement, and again, their shots tend to fall randomly within it (I'm including those random jerks that sometimes occur in the last 0.3 seconds as being part of the 'arc-of-movement'). In both cases, this randomness manifests itself as 'Poisson clumping'.

If the original poster is shooting groups with a small number of shots, then the shifts in group center may be nothing more than the result of randomly pointing the gun at a different spot each time he pulls the trigger.

Regards,

Al B.

[Steve Swartz]

Alb:

I'm pretty sure Poisson Clumping does not apply here. I let it drop last time, but contact me off target talk for a detailed disucssion.

Steve Swartz

leslieswartz@verizon.net

[bryan]

Hi steve, I would be interested in poisson clumping? has it been covered before?
I was getting different groups from target to target, 10 shots each, though it is now getting difficult to score with 10 shots. thought I was mostly doing the same thing wrong for that target. then moved to split groups, 4-5 shots in a group in 2 seperate places, but as I improve my technique, this issue is largely gone, I think I realise earlier and stop doing it, so only get one shot wrong. but group centre still shifts, normally within the 9/10 ring

bryan

[john bickar]

I struggle with this quite a bit, more so with bullseye (conventional) pistol, and less so with international. The things I check when I group shifts happen to me (assuming that the execution all looks the same from my end) are:

• Stance (i.e., foot position)
  Grip
  Head position - which I check by making sure that my sights are centered in my glasses lens. This is somewhat easier to do when you use an iris, which I don't any more.

Head position, to me, is the trickiest of the three. Not only do I have to make sure it's the same from string to string, but I have to make sure it doesn't change throughout a string.

Ah well - it gives me something to think about, and distracts me from that front sight waving in the breeze like a narcoleptic chimpanzee on Ritalin.

[Fred Mannis]

Hi steve, I would be interested in poisson clumping? has it been covered before?

Discussed at great length here: http://www.targettalk.org/viewtopic.php?t=12528

[awadhnavab]

Let me clarify what I meant by 'groups'. These are 5-7 shots all grouped approximately the size of the 10 ring (meaning pretty closed groups). And each successive target that I shoot has one such group with an eccentric placement.....even sometimes somewhere in the 8 ring......Comments !

Rajat Dhesi
India

[David Levene]

And each successive target that I shoot has one such group with an eccentric placement.....even sometimes somewhere in the 8 ring......Comments !

That probably just means that you are changing something, but doing it consistently.

Follow the advice on things to check already given by others on this thread.

[alb]

Let me clarify what I meant by 'groups'. These are 5-7 shots all grouped approximately the size of the 10 ring (meaning pretty closed groups). And each successive target that I shoot has one such group with an eccentric placement.....even sometimes somewhere in the 8 ring......Comments !
India

Try shooting 50-shot groups and see if you still notice the same thing -- I guarantee that you won't!

50-shot groups will also give you a much better indication of your current skill level, particularly if you drop the worst 2 or 3 shots. Additionally, you will be able to adjust your sights much more reliably.

The average 50-shot group size is about 70 percent larger than the average 5-shot group size when shot by the same shooter with the same gun, and the variance in the size of 50-shot groups is less than half of the variance in the size of 5-shot groups.

If you do this you will find that most, if not all, of those 5-shot groups lie within the covering circle of your 50-shot groups. In other words, you're seeing random clumps and interpreting them as patterns, where no such patterns exist.

You can observe the same phenomenon by creating a Monte Carlo simulation on your computer, for firing shots at the center of a target, with the hits varying independently on the X and Y axes, with distributions for both the X and Y axes following a normal distribution. If you program the simulation for 5-shot groups, you will see clusters with their centers randomly located about the center of the target. If you then program the simulation for 50-shot groups, the clusters will disappear.

This kind of simulation doesn't involve changing grip pressure, changing stance, changing trigger finger placement, shooter fatigue, etc. -- just pure random numbers.

Of course, all of those things affect your arc of movement, which ultimately affects the size of your 50-shot groups. Better shooters shoot smaller 50-shot groups.

Regards,

Al B.