Definition of "Group"

[Rob Pincus]

Sheesh, I can't believe that I am asking this kind of a nit-picky question.. but, here goes:

On another Thread a couple of guys have made statements that seem to imply that a group is measured "around" your point of aim. I was under the impression that a group was simply measured around your holes in the target, regardless of how far the average point of impact was from the point of aim.

Confused?

IOW: If I shoot at a dot and all of my rounds are in a two inch circle that is located 10 inches to the 11 O'clock from the dot, I have still shot a 2" group, right?

Obvisouly, I am not within 1 inch of my point of aim, though a sight adjustment should make that possible, right?? Is it still "okay" with rifle guys to refer to the original group as a " two inch group " or do I need to be "on target" before I can really proclaim a true "group" ??

I have always figured that a group was measured to show the potential of the rifle, while the difference between point of aim and point of impact (ie- hitting your target) was more indicative of shooter skill.

I just wondered, so that we would all be on the same page.

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-Essayons

 

[Rosco Benson]

A group's size is simply the distance between the two outermost shot's centers. Typically, this is established by measuring to the outside edges of the two outermost shots and then subtracting the bullet diameter. The "size" of the group has nothing to do with its relationship to one's aiming point. In most cases, the shooter will want to adjust his sights so as to cause his group to coincide with his aiming point. This is called "zeroing" the piece.

For example, a shooter testing several different loads for their accuracy potential might fire a group with each...noting the group size, but not caring whether the group was on his point-of-aim. After determining which load he prefers, he would then adjust the sights to zero the piece with the selected load.

"Marksmanship" is so called because it involves hitting a "mark". Most contests have evolved to reward hitting as close to one's intended mark as possible (the 10-ring of a target...even the x-ring, if possible).

Rosco

 

[Rob Pincus]

Roscoe,

That's what I thought, but, frankly, you threw me when you said to another member that his 4" group meant he was hitting within 2" of his target. For some of the people that are just getting into rifle shooting, I ddin't want them under the impression that if your rifle wasn't on the target it was worthless.

I have seen people get very frustrated by rifles that shot awesome groups, but they had trouble "zeroing" it. They almost always end up blaming the rifle or their skills as a shooter, rather than seeking help in the aligning of the point of aim and the point of impact.

Thanks for the clarification.

 

[Bushwhacker]

This is what I really like about the TFL group, Ilearn something here everyday. Thanks.

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Justice for one,Justice for all.

 

[Rosco Benson]

Rob; You doubtless know the old saying about what happens when we "assume". That's just what I did with my earlier statement. Strictly speaking, I should have said that if one has a 4" group, WELL CENTERED AROUND ONE'S AIMING POINT, then the shooter is hitting within 2" of his point of aim. I assumed a zeroed weapon.

Unzeroed weapons are a drag. Sometimes the zeroing process can be frustrating. SOme scopes are not "honest" in their adjustments, some metallic sights are very "coarse" (slide and clamp, for example) and, thus, difficult to finely zero, and some rifles will shift their zero from week to week due to stock warpage or other problems. The shooter who is interested in hitting (and not just making noise) will take the time and effort to refine his zero so that he KNOWS if he misses it was "pilot error", not an unzeroed gun.

I recall hearing a story about how, during the Vietnam war, an officer was hurrying to board a chopper to go to a battle that was underway. He had grabbed an M-16 that belonged to somebody else and he paused briefly, while running to the chopper pad, to take a couple shots at a dusty spot on a hillside some distance away. Seeing the dust fly from his hits, he knew that the rifle was zeroed...at least well enough to be useful...and boarded the chopper.

I read, in an article in Tactical Shooter magazine recently of a police sniper instructor who had a group of students arrive who had no idea that their scopes could be adjusted to zero their rifles. They had simply mounted their scopes, determined where their shots hit in relation to the crosshairs and had been "holding off" to correct. Sheesh!

Rosco

 

[Rob Pincus]

I got into a 2 hour argument with a gorup of guys at a hunting club last fall about zeroing.

I was with my wife and a friend and we were at the Club's range sighting in her new BlackPowder rifle at 50 yards.

She was off to the left, but her group was good. While she was shooting the firs few rounds a couple other members of the club showed up. My friend is an avid hunter, but not an avid user of iron sites. We were his guest at the club.
The other two guys and my pal all went with us to examine the group and on the way back one of the other guys offered to adjust her rear sights. Well, who am I to interfere with this guy trying to be helpful, so I figure.. Cool.. smoke break... and get away from the black powder...

When I get back over there he is finishing up and my wife is ready to reload. She fires three shots, none of which hit the paper. Right about now I am thinking that I need to get on the sights and fix things, but the guy who adjusted the rear sight insists on shooting the gun. He fires and misses. He fires again and misses the paper. He and his buddy head down to the backstop to put up a larger peice of paper, meanwhile I ask which direction he had moved the sight. Sure enough he had moved it to the left. To make matters worse my buddy thought that he was correct to do so!
Those two come back while we are arguing about which direction to move the sight and they all three assure me that they are hunters and you always move the rear sight inthe direction that you are off.

I try logic, by using the ram rod to demonstrate the line of sight, etc, but it falls of deaf ears. So my wife and I just left them with the rifle and I let them have at it.

5 shots and 2 sight adjustments later, I finally got them to align the point of aim with the orginal point of impact (from my wife's first three shots). That meant moving the rear sight in the opposite direction, of course.

Then I explained how you move the point of aim back to the desired point of impact with the muzzle in tow. All was well, though only my friend ever apologized for making the mistake. The other guys just walked off.

Remember, when sighting in, you can change the point of Aim without moving the rifle (just the sights), not the point of impact!

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-Essayons

 

[GLV]

Four inch group at 100 yards? Here in Indiana, we call that a gathering.

Seriously, a group is a group regardless of aiming point. From Standards&Practices Reference Guide for Law Enforcement Firearms Instructors, Group-a bullet group, the pattern of bullet holes in a target. GLV

 

[Daniel Watters]

This thread reminded me of something interesting from my old high school physics text. The authors defined the difference between 'accuracy' versus 'precision' in measurements. They actually used a firearm analogy! (Alas, this was many years ago.)

'Precision' refered to repeatable results in measurements: the example being a tight group.

'Accuracy' refered to how close a measurement was to the actual figure: the example being a well-zeroed grouping.

The text made the point that you can be precise without being accurate, and accurate without being precise. (Forgive me if I've reversed the two, but it has been a long time.)

Best wishes,

Daniel