What and how to measure a shot group

What the heck's the use of firing five shots for groups, if you're going to "cherry-pick" the best three??
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Well if you are shooting bullseye they all count.

If you are shooting to try out a new gun or load the 3 of 5 method helps. But it helps only if you keep track of both. You count your flyers, but they count as your flyers. The point of the 3 and 5 is to isolate the shooters error from what the gun/ammo can do. You look for consistency. It's one tool in the tool box.

By the way, this method predates Ayoob. He borrowed it, I believe, from bench rest rifle shooting and the methods used to test rifle accuracy at 100 yards and beyond.

Personally, I never shoot for groups. I shoot to hit a target and aim to place each shot where I want it. Groups are the result.

If I comment on a group I've shot I always say "5 rounds in 3.5 inches, 3 of which were inside of 2 inches" or " A good 2 inch group spoilt by my two flyers that opened it to 4 inches". If I were to only mention the 3 best shots it would give a distorted impression of my own abilities something I have no need to do. But citing the 3 best gives someone a better idea of what the gun and ammo can do, IMHO.

tipoc
 
Flyfish,

Your points about why traditional group size isn't an ideal measurement are all on target. (Sorry 'bout that. :o )

However, coming up with your own method for measuring groups is also problematic because no one else can compare their results to yours or vice versa.

The military has developed a few standards (CEP, R95, RMS, etc.) for measuring accuracy that answer your objections. Unfortunately, none of them are anywhere near as easy to use as a simple group size measurement.
 
John, thank you for the reference to those military standards. I'll track them down. I did see one or the other of them discussed in one of the AR forums a while back, and it sounded very similar to the method I developed independently, although somewhat more sophisticated (no surprise there).
 
Not to be argumentative, but I'm still of the opinion that the purpose of a five-shot group is not just to test the shooter, but the rifle, as well. When I say I've shot a .226", five-shot group @ 100 yds. with my rifle, the .226" measurement would include the "flyers". :) Shooting five shots, then throwing out the two worst doesn't test either the rifle or the shooter, as there's no empirical method of determining whether the rifle or the shooter's responsible for the "flyers". Why best three? Why not throw out three and count the best two??
 
I always thought the test of a handguns accuracy was taking into account all the ammo it holds, and find your grouping for that. So if you have a 6 shot revolver, how close are all 6 shots, and if you have a 15 round 9mm how close are the 15 rounds. Maybe others will think it is dumb, but that is the method I measure from. I am not a great shot, so I just tell everyone I am cheap and like to be able to reuse my targets. :rolleyes: So I just measure the dents in the sandbank--yardstick works very well.
 
Novalty, +1 on the yardstick and I agree on firing all chambers in a revolver as each is essentially a different gun.


My thinking, faulty as it is, is that we are attempting to determine the the accuracy and precision of the system composed of the shooter, rifle, sighting system, and ammo at a given altitude under ambient atmospheric conditions (with probably a few more variables). My purpose in doing so is to evaluate reloads, sight a scope to a particular distance, or just having fun. The accuracy is where the group centers and the precision is determined by the size of the group, right?

Once the above is done I then need to determine how good I am at putting the first shot dead center on aiming point from a cold and clean barrel. This is relevant as I use my rifles, even 22s, for hunting and the cold and clean are the conditions when I make a shot at game. This requires either a second trip to the range or packing the cleaning gear and waiting until the barrel returns to ambient temp.

Any thoughts on the above?:confused:
 
The military has developed a few standards (CEP, R95, RMS, etc.) for measuring accuracy that answer your objections. Unfortunately, none of them are anywhere near as easy to use as a simple group size measurement.
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I've had a chance to look into the standards you cited. They all derive from exactly the same procedure of measuring the locations of impact and then calculating the group center that I described. The only difference is that the military is using the variance (standard deviation, if you like) to calculate the size of a circle that will contain a specified fraction of the total impacts (CEP = 50%, R95 = 95%, RMS = approx. 67%).

I had suggested that, with the same information, you could calculate the probability of hitting a target of specified size, which is arguably of more interest for a hunter. It's exactly the same procedure statistically, just simply a matter of how you frame the question you want to answer. But, no matter which way you go, the first steps are the same - measure the location of the impacts, calculate the group center, and then determine the individual variation of each impact from that center.
 
+1 on olmossbak's post.

I mentioned earlier that the 5 round shot for group size and the 3 and 5 method are just 2 tools in the tool box. There are others that let you know other things.

Back in the day, before telescopic sights on handguns, bullseye shooters in the slow fire stages would often use only one or two chambers of the cylinder. It was and is the case that in wheelguns, one or two chambers are more accurate with a particular load than the other chambers in the cylinder. How do you know which ones? It takes a lot of shooting. It takes the shooter knowing the difference between the shooter tossing a flyer and the gun doing it. Some shooters numbered their chambers to keep track.

Temperature is important to bench rest shooters as well as hunters. 3 rounds are often used in sighting in scopes if the shooter knows the rifle and ammo. A rifle hunter often only fires 3 rounds in testing ammo, allowing the barrel to cool in between.

If you shoot 5 rounds out of a semi, and you have some experience shooting, you know which you tossed an inch wide and which the gun tossed, if any.

If you look at gun mags you'll note that in tests of the accuracy of guns and or ammo 5 round groups are always cited and often the best 3 of 5 cited as well. They often also mention the number of 5 round groups shot and average out the difference in group size in presenting their figures. This practice goes back decades and is custom. In a revolver all 6 chambers are fired in testing.

By the way, you don't "throw out" the 2 flyers in the 3 and 5 method, they are counted too and mentioned.

The 5 shot group and the 3 and 5 tools are usually shot from a bench rest the aim is to evaluate a given load in a gun and to eliminate the influence of the shooter as much as possible. Same as with a ransom rest. Multiple 5 shot groups are made with the same load.

There are other tests of accuracy that test the shooter as a factor as well as the gun and ammo.

Once you get much past 5 or 6 rounds in a 2"x2" target it can get hard to see the holes depending on what you're shooting.

tipoc
 
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