I see a lot of posts and articles in which someone has taken a new barrel (or full rifle) out to measure accuracy, but they rarely post too many details about how is it done other than the range.  I understand the basic math behind, like what one MOA (or 1/2 MOA, 2 MOA, etc, etc) means, but what is generally used (optics, etc), how is it used and what exactly is measured?

For basic checks, it seems that 100 yds is typical range, but is that mostly influenced by available ranges?  A few that I've seen mention the scope used where around 6x when shooting at 100 yds.  Is that typical?  Are groups shot from a rest (or improvised rest like a range bag, in a pinch)?  Seated?  When measuring, do you use the largest center-to-center measurement from within group (which would also be the smallest diameter of a circle that includes all of the centers)?  Does it depend on the size of the group?  For example, it seems that people include all of a five-round group, but with a larger group (say 10 rounds), there often seems to be another number that includes most, but not all of the holes.  From a sampling perspective, that would make sense, but what are the common rules?

If you want to do it the real, statistically valid way, look up "Calculation of Mean Radius of a Group".

It is a huge pain in the ass, but the results are interesting, and more valid than just selecting the groups you like, or drawing a circle, or measuring the outside holes.

Also, groups measure precision, not accuracy.

I teach applied statistics, so I figured that there was a more technical calculation.  However, I also know that technical ways tend to be ignored in practice because ... as you say ... they are a pain in the ass.  I will check it out, though.


Where's the face palm emote.  I actually have a section in one of my courses where I discuss the difference between the two.

The common rules:

1. Sit at a bench with the rifle on the bench.
2. Support the rifle. This is usually with sandbags. Put the front bag as far back toward the action as you can. Use the rear bag to control the point of aim by adjusting it and squeezing it.
3. Shoot at least five shot groups. Seven to 10 shots groups are better statistical indicators of the precision, accuracy, groupiness, or whatever you want to call it of your rifle and ammo combination.
4. 100 yards is a good standard. It's long enough for variables to influence the point of impact, but not so long that wind gets hard to control for.
5. Measure the extreme spread of your group by measuring the outside edges of the two bullet holes that are farthest apart. Then subtract the diameter of your bullet. That gives a you a center to center measurement of your extreme spread. Don't ignore any of the shots in your group.
6. Ammo is very important. If you're shooting a group to measure it, use only one kind of ammo for that group.
7. Shoot whatever magnification makes you feel good.

Thanks!  That's about what I figured.  I was plinking for fun at indoor range using iron sights while standing and managed 3-1/2" groups at 25 yds (14 MOA), so I figured that the usual process had to be a lot more controlled/aided than that.  Next time, I'll try it on a rest and then maybe throw a little magnification (using a 1-4x scope) and see how they tighten up.

1.  I don't shoot well from a bench.  I prefer laying in the prone with a bipod and a squeeze bag or dog ear bag to stabilize the rear of the gun.  I have a range that it is more than acceptable to do so.  Other people are stuck with benches and have always shot that way.  
2.  Damn right support that bad boy.  There are some great rests ect out there but you can get away with it with cheap sand bags.  Socks filled with sand, bird seed or airsoft bbs work great for filler.
3.  5 shot groups work well if you do them multiple times.  If you follow molons writings which I will link at the bottom you will see he promotes 10.  I disagree slightly with newer shooters because many people feel the need to shoot the group fast for no reason.  6 groups of 5 is a great way of going about business in my eyes.  Do something between the groups and allow the gun time to equalize and cool.  Use a sharp aiming point.  Many people try to shoot a large bullseye which can work fine but a pointed target is best.  Target the very sharp part of the diamond or triangle and you will have the sharpest result.  This is the literal meaning of the aim small miss small adage.  
4.  100 is good for magnified optics but your shooting range will dictate.  50 yards is a good distance for testing red dots and irons.
5.  yup you can do mean radius as well which you will see in molons posts.
6.  ammo should be limited down to the lot or same box if possible.  
7.  More magnification can be a bad thing.  The sharp aiming point and magnification can help but at the same time if you attempt to muscle the gun and force it onto the sharp point you end up doing more damage than good.  Allow the rests to do work and get groups that way.

The gospel according to molon

When it comes down to it getting an idea of what your gun is capable is in a big way just finding what you are capable of.  Having someone else with you that happens to have a very high quality rifle can give you a base line.  I for one know I am capable of shooting at about a half MOA.  I know how very hard this is and how hard and long I had to work to get to that.  It doesn't sound amazing but it is my baseline and I know that I am personally able to do it.  On my best day of shooting to the standard of the MOA all day challenge found here using a bipod and a squeeze bag I was able to record a .46 moa group with a very expensive gun and handloads I made specifically for the gun.  With that knowledge of what I could do I now know what guns I am shooting can do by comparing them with that ability.  Molon does this with several of his ammo reports where he will show a group he shoots first with a custom tailored handload then compares with a factory load.  Many times we go through great lengths to attain the last few tenths of an inch at 100 yards.

Compare and contrast with yourself while being a student of the gun.  Knowing what you can do with a rifle is far more deadly/impressive than simply owning a rifle someone else has told you can shoot well.