What and how to measure a shot group - Page 2

olmossbak · May 27, 2009, 09:54 AM

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?

FlyFish · May 27, 2009, 10:45 AM

Quote:

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.

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.

tipoc · May 27, 2009, 04:55 PM

+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

Doodlebugger45 · May 27, 2009, 05:51 PM

This is why I prefer 1-shot groups myself. There's no math involved and they are all less than 1" (unless I miss the paper).

May 27, 2009, 09:54 AM	#26
olmossbak Member Join Date: May 19, 2009 Location: NE Tenn Posts: 22	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?

May 27, 2009, 04:55 PM	#28
tipoc Senior Member Join Date: December 11, 2004 Location: Redwood City, Ca. Posts: 4,114	+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

May 27, 2009, 05:51 PM	#29
Doodlebugger45 Senior Member Join Date: April 15, 2009 Location: Wyoming Posts: 1,717	This is why I prefer 1-shot groups myself. There's no math involved and they are all less than 1" (unless I miss the paper).