Posted: 10/28/2005 8:04:55 AM EDT
How do you measure group size? I understand you measure the out to out and deduct the bullet diameter, but do you do so horizontally or vertically or just whereever the furthest holes are apart, say diagonally? At one time I was told to measure horizontal only, and there's the problem. I have one rifle that will string vertically with all holes perfectly in line, which pisses me off but thats another story Measuring a diagonal group I would think one would simply plumb down from say, the highest left shot to the lowest right and measure horizontal. I dunnoWhat do you think? |
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It varies. For example: [-----------------------------------------------------------------------------------------------------] If you're talking group size on the InTarWeb, the distance shown above is .027", or .001 MOA, since you're a DeltaSealDSS-SuperSecretSpaceShuttleDoorGunner and all. However, if you're trying to impress the ladies, the distance shown above is 11". YMMV. |
lol related question. When talking MOA Accuracy and you say that a rifle is 1.5 MOA accurate. Does that mean it puts rounds within 1.5 inches of the aimpoint, or shoots 1.5 inch groups? |
Good example, thanks for the quick replies. I wish I was a DeltaSealDSS-, unfortunately I just a super(secretspaceshuttledoorgunner) Ihaven't yet got my "super" clearance yet. It's an interesting story, they recruited me right out of highschool back in '89, I'd love to tell you but you know.............. |
<--- Gives secret handshake. |
Accuracy is group size, precision is distance from aiming point. |
OK, I'll im you the story.........for security reasons, we can't trust just anyone  Where in the hell did I come up with plumbing down from the highest diagonal point and measuring accross  edited for sp |
It is possible for a rifle (or anything else, for that matter) to be accurate but not precise, precise but not accurate, bothe accurate and precise, or neither accurate nor precise. Accuracy and precision are usually independent functions. MOA is generally used to describe the precision of a rifle. Once you have tight, precise groups, making the rifle accurate is simply a matter of adjusting the sights. |
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When the audience is someone other than just yourself, you should measure from the outside to the inside of the 2 farthest shots. That is called "Extreme Spread" and that is how Benchrest is scored. Everbody is familar with it. For your own personal use you should use "Mean Deviation". This number is the average distance of each shot from the group center. While Extreme Spread only takes into account 2 shots, Mean Deviation accounts for all shots. Mean Deviation is a superior way of evaluating accuracy of guns and loads. Mean Deviation is the standard used to express all small arms and ammunition accuracy requirements for the military. |
Makes sense to me |
Well put.  (we need a clapping hands smiley) |
Man you must have a HUGE screen, my dick is longer than the line on my screen and it aint no god damn 11 inches. |
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Measure the two farthest shots regardless of where they're at (horizontally, diagonally, etc.) I found this very handy for measuring group sizes:  Brownells Group Gauge |
Cool, but whenever I order from brownells, thing tend to get out of hand 
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Well it depends on who you are... If you like most posters here you tape over the flyer holes with black tape and measure the resulting group. Usually something in the sub MOA area. then you take digital shots of your firearm and target and post on arf.. Everyone says WOW cool but my gun is more accurate. Then they post Pict's of targets that have been poked with a chop stick. Ok the real way to measure is.. A caliper.. Farthest hole to farthest hole, outside to outside... Take distance and subtract Bullet dia. This is your group size. Now shoot 10 more groups and do the same measurement. Now take the average of the 10 groups. that's when you say... Fat_McNasty, that gives me a 2" avg... Yup! that firearm/you combo will do a 2" group at any time. Well that is the breaks... |
Except the holes aren't bullet diameter.  That's why you either measure the actual size of the holes and subtract, or just skip all that and measure outside to inside. |
Well use the chop stick then... This will get you close.. If you shooting to the point where .025 or so makes a difference then you need to shoot competition! |
 You got me! I do! |